An Orkut based virus/worm appears to be on the loose, it propagates by posting notes on people’s scrapbook. So chances are that if you got a new scrapbook item on your long-unused Orkut it is because the worm has infected one of your friends there.

The virus/worm utilizes javascript code to propagate. The source of it can be found here: hxxp://files.myopera.com/virusdoorkut/files/virus.js
Update: Google apparently is actively deleting items from the scrapbook of people that were infected and that have infected others.

Update 2: More details can be found here: http://antrix.net/journal/techtalk/orkut_xss.html