The Storm worm is resorting to its old tricks in time for Valentine's Day, researchers have warned.

Security firms including Symantec, F-Secure, Sunbelt Software and Sans Institute said that the infamous Trojan is disguising itself as a Valentine's Day greeting card.

The user will receive an email with subject lines such as 'sent with love' and 'falling in love with you'. The content of the email is a single image along with a link to a web page.

Users clicking on the link are prompted to download an executable file containing the malware. A similar tactic was used to spread the worm last year.

"The social engineering attack is the same as before," wrote Sans Institute researcher Bojan Zdrnja in a blog posting.

"The subjects are almost the same and the only difference is that last year Storm sent itself as an attachment."

The new attacks come as Storm nears its first anniversary. The Trojan surfaced last year hiding itself as a video claiming to show flooding caused by extensive storms in January 2007.

Storm has since used a variety of exploits and social engineering tactics to construct a huge botnet which experts fear is now being rented out for other criminal activities.