On Tuesday security vendor WebSense issued an alert warning that holiday coupon e-mails from familiar companies may be malicious code in disguise, in this case a mass-mailing e-mail worm.

The warning cites one spoofed McDonald's e-mail that claims to present their latest discount menu, and asks the recipient to print out the attached coupon. A similar mailing pretending to be from Coca-Cola asks recipients to print out details about their new online game, and also offers recipients a chance to win Coca-Cola drinks for life. Websense says the attached zip file contains files named either coupon.exe or promotion.exe, both of which contain dropper files for remote access Trojan horses.

Previously, Websense issued an alert for a holiday-themed animated postcard.

On Wednesday, McAfee identified a third holiday-themed e-mail using the Hallmark brand. McAfee has named the malware used as W32/Xirtem@MM and says this particular worm carries a built-in SMTP engine that mass-mails copies of itself to e-mail addresses harvested from an infected machine.

In all cases the e-mail appears to be legitimate, using images taken from the McDonald's, Coca-Cola, and Hallmark sites.

To avoid compromise, antivirus experts recommend not opening e-mail attachments as well as keeping your desktop's antivirus protection up-to-date.