Just heard about this one (from Evesham) and thought I would pass details on...
Please beware of security update emails, supposedly from Microsoft inviting you to download and install a security update.
Gigger, which uses a combination of Microsoft Outlook and mIRC (internet relay chat) to spread. It is not spreading widely, but its destructive potential has prompted Symantec (Norton) to issue a strongly worded warning about the worm:
The virus is normally distributed via an email and attachment and attempts to pass itself off as a security update from Microsoft. All Microsoft's advisories are however issued via its web site or Windows Update facility and never by email.