If you unexpectedly receive a Valentine’s Day e-card, give it a close look before you get sentimental. It may be a stealth virus called the Storm Worm.

With lovers expected to express their feelings on Thursday, the FBI is warning about spam e-mails spreading the Storm Worm. The e-mail directs the recipient to click on a link to retrieve a bogus e-card. Once the link is clicked, malware is downloaded and the recipient’s machine becomes part of the Storm Worm botnet.

A botnet is a network of compromised machines under the control of a single user. Botnets typically facilitate criminal activity such as spam, identity theft, denial-of-service attacks, and spreading malware to others on the Internet.

“The Storm Worm virus has capitalized on various holidays in the last year by sending millions of e-mails advertising an e-card link within the text of the spam e-mail,” The FBI warned in an advisory. “Valentine’s Day has been identified as the next target. Be wary of any e-mail received from an unknown sender. Do not open any unsolicited e-mail and do not click on any links provided.”

Same Old Storm Tricks

Indeed, security firm Sophos has reported that virus writers are increasingly using love, money and lust to encourage victims to activate malicious code. Sophos says the latest variation is a romantically themed e-mail with subject lines such as “I Like You,” “Powerful Love,” “Tower of Love,” “You Stay In My Heart,” “Hugs And Kisses,” “Val-ANT-ines,” “Just You,” and “What is Love?” The e-mails look sweet, but contain a nasty payload — the Storm Worm.

Every year in the run-up to Valentine’s Day, people let their guard down and are fooled by hackers and cybercriminals using the cover of romance, according to Graham Cluley, a senior technology consultant at Sophos.

“You would think that people would learn,…