In June, 1999 the Internet was hit by an e-mail worm even more virulent than Melissa. FAQ (Frequently Asked Questions)
Q: How many sites were hit?
A: While the worm was several times more virulent than Melissa, it didn't spread as far. Users were already burned once, and a little bit more wary. However, several large corporations (like Microsoft) did take down their e-mail servers for awhile.
Q: Why was it so virulent?
A: Several reasons. It spread using several mechanisms, not just through e-mail, but also through "File Sharing" within a WinNT environment. Rather than using Word macros, it was a full blown executable, meaning it had many more capabilities when ran. Finally, it seeked out and destroyed files, whereas the Melissa worm simply spread itself.