OK, having now had this conversation twice, I’ve gone back to the true source of all wisdom on all things viral, “Viruses Revealed.” I got it off my shelf, of course, but some helpful vxer (who probably thought he was going to harm our sales) posted it on the net, and saved David and I the bother. (Remember, this guy is a vxer, so that page may not be entirely safe.)
Michelangelo is covered between pages 357 and 361, which is slightly over halfway through the book. However, since I guess he’s missed out the index and stuff, it turns out to be at about the 3/4 mark on the page he’s created.
Anyway, Michelangelo checks the date via Interrupt 1Ah. many people did not understand the difference between the MS-DOS clock and the system clock read by Interrupt 1Ah. The MS-DOS DATE command did not always alter the system clock. Network-connected machines often have “time server” functions so that the date is reset to conform to the network. The year 1992 was a leap year, and many clocks did not deal with it properly. Thus, for many computers, 6th March came on Thursday, not Friday.