Hack the hackers (muhahaha)

it is a rare occasion indeed when there is some fun to be had with your own web page being scanned.

i *heard* (heard!) of some occasions (a few years back) where bad people wanted to attack a website and as an example, had people go to their own page to participate in the attack. the attackers’ page in turn activated javascript code that would open several browsers going to the attacked page, thus achieving a primitive yet effective ddos.

in one such a case (youse got nothing on me!) javascript code was added to the page being attacked, which would in turn would open countless windows going to the attackers’ page from which they directed the attack [muhahahahaha].

that is indeed ddos and therefore bad, period, but there are subtler approaches yet… and morality is something yet to be decided. after all, neutralizing your attacker or someone about to attack you is pure self-defense.. ain’t it? :) at least as long as you don’t hurt others while you’re at it.

well, today i saw this:
http://www.securiteam.com/windowsntfocus/6r00b2aeuk.html

appscan has a remote exploitable vulnerability. you can create a special “present” on your page, and when it is being scanned uninvited, you can get appscan to do something naughty. ;)

as an example, email the fbi with an automatically created self-confession to scanning your site aggressively for vulnerabilities (casing your store!). you can do a lot worse but this sounds to me like so much fun i actually am considering coding it!

any takers??? :)

(this idea comes from a somewhat deranged conversation between noam, aviram, ido and me)

gadi evron,
ge@beyondsecurity.com.

Share
  • NoPh0BiA

    word.

  • http://www.BeyondSecurity.com aviram

    Lets not forget tcpdump’s famous bo vulnerability, which allowed you to own anyone sniffing on your network:
    http://www.securiteam.com/exploits/5OP0E1535Q.html

  • http://orkut.com KISHORE

    i am getting caption when trying to login orkut that this site is banned muhahaha

  • Tuttu

    am also getting such a one when i try to login to orkut and utube. any remedy

  • http://www.orkut.com Nagen

    am getting caption when trying to login orkut that this site is banned muhahaha

  • Sam

    am getting caption when trying to login orkut that this site is banned muhahaha

  • http://www.orkut.com karthi

    i am getting a caption when trying to login orkut that the site is banned MUHAHAHA

  • sonu

    even i m gettin such caption when i try 2 login orkut. ne remedy …

  • http://dipeshjkjainrediffmail.com dipesh

    my orkut is not show & say muhahaha orkut loogin not have

  • praveen

    am getting caption when trying to login orkut that this site is banned muhahaha

  • Deepika

    i am getting a caption when trying to login orkut that the site is banned MUHAHAHA

    How do I solv ethis problem.

  • http://JINDAL0200 MOHIT

    SAME PRBLM 2 ME,NY SOLUTIONS…………..

  • http://www.orkut.com sundaram

    relice the website

  • http://www.orkut.com sundaram

    please realice the orkut website.

    Thank you

  • http://www.orkut.com sundaram

    i am getting a caption when trying to login orkut that the site is banned MUHAHAHA

    How do I solv ethis problem

  • http://orkut sunny

    unable to open

  • Paul J Alengadan

    Am not able to open orkut. Even I cannot make a file of that name.

  • http://www.skjay.info/ Jayachandra

    I have the solution for the MUHAHAHAHA problem. Visit http://www.skjay.info/

  • http://cse_012yahoo.co.in savleen kaur

    i am not login to my orkut site caption is showing site is benned muhahaha please give me any knd of solution reply soon its urgent my id is cse_012@yahoo.co.in or fantasy44@gmail.com

  • ANSHUMAN KANUNGO

    I M VERY MUCH WORRY THAT I CANNOT ABLE TO OPEN THE ORKUT.

    PLEASE HELP ME SOON.
    WAITING FOR YOUR HELP…….

  • http://s.anjelogmail.com anjelo sherin

    i am much worried since i get an capution muhahaha wen i open orkut.please help me to over come it

  • http://s.anjelogmail.com anjelo sherin

    i am much worried since i get an capution muhahaha when i open orkut.please help me to over come it….

  • http://s.anjelogmail.com anjelo sherin

    i am getting an banned message muhahaha when i open orkut.please help me to over come it….

  • happy

    i wanna to open my orkut pls

  • Heman

    Wat the fuck man!! who is doing this ? wats going on? is this a virus ? or this is some hacker? who are u man???!! i am on u….will get u for this!!! start crying…or praying!!!

  • MAYANK

    same prob here guys……………

    how to overcome it…plzzz help me

  • Prathiba

    Hey people even im gettin the same message box…………..”ORKUT IS BANNED”……….wats going on.???????…nyways think it will help us to get out of dis ‘orkut addiction’…:)

  • praveen

    get NOD antivirus….and have a full scan of system……..then go to quarentine folder some where in C-drive……then delete all the files from it …… thts how i got rid of dam virus………….the javasript is in the name of ‘HEAP’……

  • gurveer singh

    are yar m fedd with all this ne solution or wat else we shud do

  • http://www.orkut.com SUNNY

    I have the same problem with Orkut.
    That it was saying it was banned MUHAHAHA!!

    I’m not getting the perfect idea what to do to overcome this.

    Can any one suggest me here plzzzzz.
    “gsrbtech@yahoo.com”

  • http://www.orkut.com SUNNY

    How to Remove…

    The Orkut Virus which also affects the U-Tube and the Mozilla Firefox

    Have you experienced the new ORKUT virus which is quite annoying ? It does not allow the words Orkut or Utube to be typed on the address bar of your IE window. The browser simply closes the first time. But from the second time, strange messages come with the violent laugh MUHAHAHAHAHA!

    The virus creates an svchost.exe file which is memory resident and does the above task of preventing Orkut users. The svchost.exe is an essential file for the switching on of any WinXP computer and if it is damaged then the computer will not boot.

    But this svchost file comes with the user-process rather than the system process. So, when you open the Task Manager, and view the processes, the user name will be your user-name and NOT SYSTEM, NOT NETWORK etc.

    If you find such svchost.exe then your computer is infected with Orkut virus.

    Prevention

    The virus travels through Flash-drives. The Flash or Pen-drive will have a new file, Microsoftpowerpoint.exe which when double-clicked spreads the virus. therefore whenever you find such file, just don’t open but delete it.

    Removal

    To remove the virus, open the Task Manager, by pressing Ctrl-Alt-Delete and examine the processes. There will be several svchost.exe files. Ignore them and focus on svchost.exe with username as your username. (Sometimes it may be administrator if you have not created a user name at all).

    End such svchost process by selecting it and clicking “End Process”. Then type orkut in the explorer’s address bar and nothing will happen.

    Then goto system32 folder, identify svchost.exe file with a prefix icon H and delete it.

    Then run regedit and search for “heap” repeatedly and delete all “heap” folders and values. The virus stands removed.

    ***

  • mukul the genius

    just restore your computer to an earlier date…this “brontok muhahaha” virus leaves a sign in ur registry…so restore to an earlier date and registry wil be clear.

  • Karthick

    i too had tha same problem.
    i tried AVG spyware wic is a 30 day trial version.
    it removed all the infections from my system.
    if u trust me try it

  • http://www.orkut.com poornima

    iam getting problem from you
    orkut is banned wii be coming

  • http://orkut Anurag

    hey dude mah orkut is not opening i m not able 2 login so plez du nything bt plez rescue mah orkuutt
    mah id is……………anuragverma398
    @gmail.com

  • http://www.orkut.com Harsha

    i am not able to open my orkut acct plz help or give any solution

  • shruti

    Hey dude my orkut is not opening i m not able 2 login so plz do something plez rescue mah orkut i will thankful .

  • http://www.orkut.com sunny

    Hey dude my orkut is not opening i m not able 2 login so plz do something plzzzzzzzzzzzzzzzz
    my id is …………..sunny01jha@gmail.com

  • gurveer singh

    thanx buddy sunny reaally thank u .guys jst do as sunny said you ll b more than happy

  • Goutham

    Bro i tried doing as sunny said bt the process re appears again and it shuts down immediately….

  • Goutham

    Hey sunny thanks… Guys do wat sunny has mentioned… Everything will be done…

  • manoj

    i tried doing as sunny said bt it shuts down immediately…. wat 2 do please reply quick
    wayne.mans@gmail.com

  • http://orkut kashior

    muhahaha

  • http://orkut swaminath

    opend the orkut

  • http://orkut swaminath

    opend the orkut muhahaha

  • Saraswathi

    Hey thanx SUNNY……………..orkut opened.thanx again dude!!!!!!!!!!!!

  • Samuel

    To remove the ORKUT BAN…
    Open search from Windows Explorer.. search all files and folders for “*.exe” (without the ” “) look for svchost.exe with the “H” icon.. right click on it and open the containing folder.. Delete all the files in the folder.. u many not be able to delete them all.. Restart your computer.. You would get an error message on restart.. ignore it…
    Open regedit.. scroll to hkey_local_machine\software\microsoft\windows\currentversion\explorer\advanced\folder\hidden\showall.. and on the right side if the screen.. right click on checked value and modify the value to “1″.. search for “heap” in Registry Editor and delete all folders and entries… Restart your computer again.. You will then be able to see all the hidden files under c:\..
    There will be a folder named “heap42a” or sumthin like that which would be hidden… try and delete that folder…

  • Sunboy

    I serached for the file svchost.exe and could only find one entry under the folder C:\WINDOWS\system32 and this file did not have a ‘H’ icon associated with it. I tried cleaning the registry by searching for the Heap folders and deleted them off but still the problem persists. When I log back again into the machine the svchost.exe process is again associated with the user id I log in with. Any suggestion for the same?

  • Prakash

    Hi..guyz,

    Am also facing the same pblm. But am not able to open “regedit”. this Damn virus is not allowing i guess. Any idea on that ?

  • anshu

    i always get a caption written that my login to orkut has been banned n it has been done by muhahaha….pleeeez give a solution as soon as possible…..

  • Mujeeb

    i am getting a caption when trying to login youtube that the site is banned MUHAHAHA

    How do I solv ethis problem

    any 1 can help me plz……………………………..

  • http://orkut rushikesh nisal

    I am not able to open orkut on my laptop. Whenever I try to open the orkut web page i get message “This site is blocked & script is written by MUHAHAHA”,

    Kindly help me on this problem , I cant communicate with my friends.

  • sam

    i can’t access my orkut account…when i try muhha displayed orkut is banned…plz help me

  • sam

    plzzz give me solution to open my account

  • http://orkut,youtupe uma

    am getting a caption when trying to login youtube that the site is banned MUHAHAHA

    How do I solv ethis problem

    any 1 can help me plz……………………………..

  • http://nil afzal

    i can’t access my orkut account.when i try muhha display orkut is banned plz help me what can i do

  • http://orkut&youtube hemanth

    that stupid virus has banned access to “task manager” & regedit.. i use the AVG antivirus free version .. i also scanned the whole system, but it din’t detect anything.. guys .. any 1 out there.. plz help me get rid of this muhahaha!!!! virus..

  • http://orkut Aniket

    can u help me as m not able 2 open orkut due to the Muhahaha virus is there an way by which i can open ma orkut account

    Regards

    Aniket

  • arijit

    i cannot open orkut so plez help me

  • farooq

    pls get me orkut back

  • saj

    pls get me orkut back

  • VAISHAKH

    it shows orkut banned witha big………………muhahaha

  • Nandana

    just restore ur computer some previous date

  • ranabs

    can u help me as m not able 2 open orkut due to the Muhahaha virus is there an way by which i can open ma orkut account

    Regards

    Ranabs

  • http://yahoo nancy merriman

    Thanx a lot, Sunny . That spooky MUHAHA has at last left our PC. We just followed ur instructions. Man, hats off to ur grey cells.

  • anand

    im unable to open orkut and you-tube, plz help me, to remove the script……

  • Shyamji

    im unable to open orkut, plz help me, to remove the script……

  • http://orkut yakshit

    I am also not able to login orkut
    after adding caption orkut i get msg orkut is banned muhahaha

  • prasad

    can not open orkut one message displayed muhahahaplz help

  • http://resawalyahoo.co.in satish

    can not open orkut one message displayed muhahahaplz

  • http://hi satish

    can not open orkut one message displayed muhahahaplz help me call me 9325037220

  • http://orkut.com,youtube.com Bharat

    unable to open

  • Anup Kumar Shah

    i can’t access my orkut account…when i try muhha displayed orkut is banned…plz help me

  • Kalpan

    After the PC is got affected by MUHAHA , I can’t see the hidden files, so i can’t find the folder heap41a, and one more thing any pen drive or chip is not openning by double click, to open it one should use right click>explore. Any antivirus or spyware released to block till now?

  • http://orkutandyoutube devesh bhardwaj

    After the PC is got affected by MUHAHA , I can’t see the hidden files, so i can’t find the folder heap41a, and one more thing any pen drive or chip is not openning by double click, to open it one should use right click>explore. Any antivirus or spyware released to block till now?
    The Orkut Virus which also affects the U-Tube and the Mozilla Firefox plese help me soon plz plz plz .

  • Imran

    i can’t access my orkut account…when i try muhha displayed orkut is banned…plz help me

  • Imran

    Yahoo messenger is not work due to virus.

  • dev

    I am also not able to login orkut
    after adding caption orkut i get msg orkut is banned muhahaha

  • Ashima

    i tried as Sunny said but after i stopped th proccesses again th same prob is comin when i login again..ther are no icons with H in system 32…hmmmm
    plsss tell me wt to do

  • VIVEK

    I AM ALSO NOT TO LOGIN ORKUT

  • Rush

    I cant open “Task Manager” & also regedit due to this virus, also cant see hidden files!!! Found svchost.exe in C:\WINDOWS\system32 which did not have a ‘H’ icon associated with it.. hence, also cant delete any system files there.. Plz suggest somthing soon coz i am facing problem installing othr s/ws also….

  • midhun

    i can’t open ORKUT the mesage is coming like orkut is banned muhahaha so plz help to overcome that

  • sajal mukherje

    Hi friends…i am also facing the same problem sine a week or so…..it is also forbading any searck related to orkut. The site is not getting opened giving banned…info…and MUHAHAHA…….sound….plz help me come out of the situation …..any body there….

  • Mohamid rahman

    hi!!!!
    now i am able to get orkut login page after removing “svchost.exe” in processes associated with my name….

    thanx buddy………….to Sunny

  • http://orkut tarun

    fderrwer tytry r rthyrtg rtr rty

  • Rahul

    I could not login to orkut….Any help please…

  • http://orkut hari

    Icould not login orkut pls help …………………

  • http://orkut hari

    I could not login orkut pls help …………………

  • http://www.orcut.com Deepak Kumar

    please help me against open the orcut

  • sharan

    me too got d same prob as RUSH said..
    couldn even open d task manager…
    it says, ‘task manager has been disabled by ur administrator’..

    kindly help..
    tnx in advance…

  • http://orkut narwadeshwar

    same problem plz help………..

  • http://orkut appu sinha

    plz help me orkut is coudnot be open

  • http://orkut appu sinha

    why coudnot be open orkut help me

  • http://gmail ANOOP SADASIVAN

    i cant open my orkut please help me

  • http://orkut divi

    i cant open my orkut plzhelp me

  • http://orkut divi

    orkut is not opening if i am trying to open it is saying that orkut is banned administer dint write this programm

  • http://bannedthisorkut umesh

    not opening this orkut plz help me i am trying to open it is saying that orkut is banned administer dint write this program.plz plz help me

  • http://sanjithtdyahoo.com sanjithtd

    got rid of muhahaha virus thank u samuel

  • tina

    hey………..plz help out ,,,,,,,,,,I want to open my orkut and mozzilla firefox

  • http://ORKUT SAHIL

    when i was trying ti log in i am hearing a voice muhahaha he said orkut is banned u fool hey my english is weak

  • http://ORKUT SAHIL

    when i was trying ti log in i am hearing a voice muhahaha he said orkut is banned u fool hey my english is weak sorry

  • sri

    The Orkut Virus
    How to Remove the Orkut Virus which also affects the U-Tube and the Mozilla Firefox

    Have you experienced the new ORKUT virus which is quite annoying ? It does not allow the words Orkut or Utube or Mozilla to be typed on the address bar of your IE window. The browser simply closes the first time. But from the second time, strange messages come with the violent laugh MUHAHAHAHAHA!

    The virus creates an svchost.exe file which is memory resident and does the above task of preventing Orkut users. The svchost.exe is an essential file for the switching on of any WinXP computer and if it is damaged then the computer will not boot.

    But this svchost file comes with the user-process rather than the system process. So, when you open the Task Manager, and view the processes, the user name will be your user-name and NOT SYSTEM, NOT NETWORK etc.

    If you find such svchost.exe then your computer is infected with Orkut virus.

    Prevention…..

    The virus travels through Flash-drives. The Flash or Pen-drive will have a new file, Microsoftpowerpoint.exe which when double-clicked spreads the virus. therefore whenever you find such file, just don’t open but delete it.

    Removal

    To remove the virus, open the Task Manager, by pressing Ctrl-Alt-Delete and examine the processes. There will be several svchost.exe files. Ignore them and focus on svchost.exe with username as your username. (Sometimes it may be administrator if you have not created a user name at all).

    End such svchost process by selecting it and clicking “End Process”. Then type orkut in the explorer’s address bar and nothing will happen.

    Then goto system32 folder, identify svchost.exe file with a prefix icon H and delete it.

    Then run regedit and search for “heap” repeatedly and delete all “heap” folders and values. The virus stands removed.

    ***

    Removal of MUHAHAHA VIRUS
    Please read the letter below for more detailed instructions to remove the MUHAHAHA virus

    My Dear Karthik,
    There are several types of svchost.exe in Task manager. The task manager shows the files as follows:

    svchost.exe SYSTEM
    svchost.exe LOCAL SERVICE
    svchost.exe NETWORK SERVICE ETC.

    Suppose your user name is karthik (Press start button and on top you will see an Icon followed by your user name).
    Then you will see an entry in Task manager as follows:
    svchost.exe KARTHIK

    This svchost.exe file with KARTHIK will be the virus file and this alone should be deleted. If you delete other svchost.exe files for system, network etc, your computer will crash and recovery is difficult.

    Therefore, first close the process in Task manager by pressing “End process” for the “svchost.exe KARTHIK” file only. Then goto system32 folder in windows and delete only “H svchost.exe” with icon H preceding the file. Don’t delete other svchost.exe files.

    Then press start button, click run and type regedit and click ok. Your registry will be opened. Then press F3 and find comes. There type heap and search. Wherever it stops and gives any values, corresponding to “Heap”, just press delete button on key board and delete it. Then Press F3 once again and so … on, till you delete all heap folders and values.
    Then restart the computer. Your MUHAHAHA virus is gone for ever !!!!

    This is working…..

  • pat

    good solution thru the regedit way f3 and del
    works!!!!!!!!!!!

  • shravan

    thanx

  • Ashfaaq

    Thank u guys it was very usefull .i deleted that virus.very very thanks

  • sujan

    orcut is banned you fool,administrator has not blocked you,guess who did it?…this is the message i get on opening orcut…help me out on this

  • kidu

    prevention helped. thanks a lot.

  • Maran

    Hi Sunny,

    Thank you so much…I have successfully remove and could able to see orkut/youtube and work with Mozilla.

  • http://ORKUT NAZNEEN

    I AM NOT ABLE TO ACCESS ORKUT.I AM GETTING A CAPTION THAT I CANNOT ACCESS ORKUT.PLEASE HELP ME

  • SIBIN

    i am getting a caption when trying to login orkut that the site is banned MUHAHAHA

    How do I solv ethis problem.

  • http://subhasisdasguptagmail.com subhasis

    help me to open my orkut.

  • http://subhasisdasguptagmail.com subhasis

    pls help me to open my orkut.

  • shinjan

    i have two SVCHOST.EXE files with username as india. which one i will delete?

  • prem

    hey sri……………….i dont have file name as “H svchost.exe”…..
    after goin to task manager n den deleting svchost.exe with username..da virus is goin..but after restarting pc it is coming again …plzz send me solution.

  • http://www.emphazer.com Santhosh

    Dear Friends…

    MUHAHAHA.!!!!!!!!! virus migrates thru pen drives or even thru CD’s.

    In CD’s if you find a file named Microsoftpowerpoint.exe kindly delete it.
    The virus gets installed to the computer by this executable file.

    Unfortunately if you are affected by this virus, do not worry you can still get rid of it.

    But you will have to follow the following steps.

    The following steps are in a very simple language.

    Step: 1. Click on “Run” and type the following address: C:\heap41a and hit Enter key.

    You cannot find the “heap41a” file by navigating thru files and folders using mouse in C drive.

    Inference: You will find the following files in the above path
    a) Offspring (folder), b) 2.mp3 (Muhaha laughing sound that is played while virus closes the window),
    c) drivelist (notepad file), d) reproduce (notepad file), e) script1 (notepad file), f) std (notepad file), g) Icon (Icon file)
    h) svchost.exe (executable file)

    Step: 2. Delete the “svchost.exe” file with the big “H” icon.

    Step: 3. Then press start button, click run and type regedit and click ok. Your registry will be opened. Then press F3 and find comes. There type heap and search. Wherever it stops and gives any values, corresponding to “Heap”, just press delete button on key board and delete it. Then Press F3 once again and so … on, till you delete all heap folders and values.
    Then restart the computer. Your MUHAHAHA virus is gone for ever !!!!

    Kindly send me your comments / feedbacks on this article to my E-mail ID: santhoshdts@gmail.com

    Regards

    Santhosh
    Emphazer Inc.

  • bithika

    thanks a lot to SANTOSH and SUNNY. it really works!!!!!! MUHAHAHA gone…………….

  • Ajay

    MUHAHAHA
    Thank u guys it was very usefull .i deleted that virus.very very thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks ! thanks !

  • Padmachandran

    thank you my virus has gone………

  • http://www.orkut.com ankit

    i am getting a caption when trying to login orkut that the site is banned MUHAHAHA

    How do I solv ethis problem.

    pls help me to open my orkut

  • ssg

    Hello

  • http:///www.lern2hack.blogspot.com Sriki

    Is this virus still working on orkut or it has been fixed?

  • http://www.lern2hack.blogspot.com Sriki

    Hey i have also heard about hacking orkut with a cookie script using phishing attack.Will this really works if so can you plz give me those info…

  • alvin noypi

    guys, guys,,,,relax…create a new account and log into it…
    thats the first step i’ve made..then i fix my old account using sunny’s comment…….

  • jaipal

    R/sir

    when I open orkut, there is a message.
    banned MUHAHAHA
    please help me

  • http://zubair same problem whn im open orkut there is banned muhahaha help me

    ww.orkut.com

  • http://orkut arun

    Orkut is banned you fool,The administrator didnt write this program guess who did ? MUHAHA

  • kmv

    good. it worked after closing the process and deleting the H file.

    Regedit – F3 is not showing any heap file.

  • jibin

    thanks a lot dude /
    the problem has been solved./

  • SHARADHA

    hey i too have the same prob…but i cannot delete tat file.. i m getting ACCESS DENIED…kindly help me

  • i use orkut account by gmail id but now gmail id was disabled so i cant sign in what can ido draju@in.com

    i use orkut account by gmail id but now gmail id was disabled so i cant sign in what can ido

  • muhahaha

    i dont wanna have funny but everyone since to be laughing here everytime they say something lol

  • Joshy Basil

    I am trying to log on orkut or youtube there is a message displayed MUHAHAHA!!! my computer is not working with orkut or youtube.

  • sanjith123

    thank u

  • vidhu

    “muhahaha” prblm help me please………..

  • Pinaki

    I have attacked by MUHAHAHA virus. I want to open youtube & orkut but muhahaha was banned it. So kindly help me to remove this virus.

    GOD BLESS YOU