Symantec has discovered a new worm called W32.Badtrans.B@mm which spreads via email. It doesn't rely on any particular email program to spread itself, and may appear as one of several different file names. It also drops a backdoor trojan that logs keystrokes.
To prevent infection from W32.Badtrans.B@mm, Symantec advise corporate email filtering systems should block all email that have attachments with the extensions .scr and .pif.
More information on the worm can be found at http://securityresponse.symantec.com/avcenter/