"Security experts
have said that the attack only affects users of certain versions of
Microsoft Corp.'s Internet Explorer browser...
Additionally, Cluley said that it appears that the threat only affects
Web servers running Microsoft IIS 5 (Internet Information
Services) Web Server software and not Microsoft IIS 6, which comes with
Windows 2003 Server."
Make sure you've patched IIS with the
Sasser patches. Raise the shields high on IE, or better yet, get a
secure browser. According the article, some *major* sites have been
hacked, so watch those credit card bills!
Update: According to this article on Netcraft, the trojan can be installed silently on fully-patched versions of Internet Explorer. Until the extent of the exploit is known, you may want to hold off surfing with IE.