First worm of the year?

An email worm disguised as a New Year's greeting is making the rounds on the internet.

Worm-laden messages are titled "Happy New Year" and contain an attachment called either postcard.exe or postcard.zip, according to experts at VeriSign's iDefense Labs, which provides information on security flaws and exploits. If the attachment is opened, malicious software is downloaded from the internet and can infect computers running Windows operating systems.

Once a computer is infected, it looks for open mail proxies and begins spamming mail to infect other computers. The worm is already moving quickly across the net, at a rate of five emails per second on at least one large network, according to the iDefense Labs website.

Security experts say that although the virus looks similar to the Warezov Trojan horse that has plagued the web for the past month, it is actually a new variant of the worm and has been largely undetected as of 28 December. iDefense performed a triage analysis of the threat and found more than a dozen codes were installed on a computer from several worm and Trojan horse families. More than 160 email servers are used by the worm to send out spam to potential victims, the company said.

High volumes of mass emails are usually sent around the holidays. This year has been no different, according to experts. The spike in holiday spam is largely attributed to the fact people have been more likely to open the messages.

Consumers have been shopping online more, desperate for gift ideas. They have also been expecting electronic greeting cards from friends and family. Malicious spammers have been able to exploit this expectation by designing Trojan horses that can fool unsuspecting users.

Antivirus software maker McAfee issued several advisories over the holidays, warning customers to be wary of such Trojans. Last week it cautioned users about a malicious email attachment named Christmas+Blessing-4.ppt that installs software enabling attackers to remotely access a compromised computer.

Like many Trojans, the "Happy New Year" worm is not recognised by all virus scanners, so users should be extremely cautious when opening email attachments, experts said.

Marguerite Reardon writes for CNET News.com