Security experts say that the Swen mass-mailing Windows worm appears to be spreading quickly, moving to the top of the virus charts a day after it first appeared--and even maintaining its own counter that supposedly monitors how many PCs have been infected. For information on how to combat the worm, click here. Antivirus companies warned on Thursday that the worm, variously known as I-Worm.Swen, W32/Swen.A@mm or W32/Gibe@MM.e, had the potential to spread quickly because it is well-disguised as a security update from Microsoft. It takes advantage of a two-year-old Internet Explorer flaw that allows it to execute directly from an...