eWeek: Browser Bugs Spare Internet Explorer for a Change gives some info on 4 vulnerabilities affecting:
Most Mozilla-based browsers (Firefox 1.0, Camino .8.5, Mozilla 1.6, etc.)
Safari 1.2.5
Opera 7.54
OmniWeb 5 (but not IE).

It's probably a virus.

(Just jokin' with you, of course.)

John