As Valentine’s Day approaches, users should keep a wary eye on any romantic messages received by e-mail. They could contain malicious code and computer crashing viruses.

The Nurech.A worm appeared earlier this week using this type of lure and has caused an “orange virus alert”. It still continues to spread and infect computers. Nurech.A hides in emails with subjects like: “Together You and I” and “Til the End of Time Heart of Mine”. The name of the attached file carrying the malware is always an executable file and has names such as flash postcard.exe or greeting postcard.exe.

Other malicious codes currently infecting users include Nuwar.D. This worm arrives in messages with subjects like “5 reasons I love you” or “A kiss for you”.

Events like Valentine’s Day and Christmas are usually exploited by cyber-crooks to try and spread their creations by disguising infected emails as e-greeting cards. This tactic is known as ‘social engineering’. The best example is the infamous LoveLetter virus, which caused one of the biggest epidemics in computer history.

And it’s not just malware-infected emails that are on the prowl. With people buying Valentine’s gifts, there is an increase in online transactions and consequently an increased risk of bank details ending up in the hands of cyber-crooks. Much of the junk mail that reaches users’ accounts contains links to false banking or shopping websites, where users are requested to enter confidential information such as their account number and password; the classic ‘phishing’ routine.

Last month saw virus activity on the internet increase dramatically as a result of the Storm worm and the “Happy New Year” worm.

Internet security firm Postini said that over the three-day period when the Storm worm was active, from 19-21 January, it stopped more than 29 million infected messages from reaching the 36,000 businesses it provides email security services for.

On 20 January alone Postini said it blocked almost 17 million infected email messages, nearly 20 times the average daily virus volume in 2006.

At the peak of the “Happy New Year” worm, which circulated between 29-31 December, they blocked 19.5 million messages infected with the worm and its variants. These two attacks were the largest to occur in the past 12 months.

“The explosion of botnets, millions of infected computers controlled by malicious actors around the world, has changed the balance of power in the world communications security,” said Daniel Druker, executive vice-president of marketing at Postini. “As Valentine’s Day approaches, email users should continue to keep their guard up as there are already new mutations of the Storm worm with love-related subject lines.”