An email worm, believed to have originated in Korea, is winding its way across the Net this morning.
Braid.A (aka Bridex) is written in Visual Basic and usually arrives in an email message as README.EXE attachment. The worm uses an iFrame exploit to run itself automatically on unpatched versions of Microsoft Outlook, Microsoft Outlook Express, and Internet Explorer (there's a fix from MS for this well known exploit here.)
When the worm is first run it copies itself to the Desktop as Explorer.exe, to the System folder as Regedit.exe as well as creating a registry entry so that this file is run automatically each time the computer is restarted. Braid also drops a modified version of the FunLove virus onto infected systems.
To spread, the worms scans.HTM and .DBX files for email addresses prior to sending itself out using its own SMTP engine. Braid is capable of spoofing email addresses so that, on casual inspection, it looks as if the virus was sent by the person who receives it.
If this happens it's not you who's infected, but one of your contacts.
Managed services firm MessageLabs, which was the first to spot the virus, has so far blocked 250 copies of the worm - so it can hardly be described as prolific, and poses only a moderate risk. An advisory by MessageLabs describes the format of infected emails.