"The new virus only started spreading a few hours ago," said Mikko Hypponen, chief research officer at security firm F-Secure. "The spamming started when the storms were still raging."

Mr Hypponen believes the adaptation was designed to take advantage of the interest in the storms.

Security firms advise computer users not to open e-mail attachments unless they are expecting them and to keep security software up to date.

Slave network

Malicious coders often take advantage of celebrity names or large news events to spread viruses and worms.

in 2005, an e-mail scam offering regular news updates following Hurricane Katrina spread a virus that allowed hackers to take control of a computer user's files.

"Malware writers will use any newsworthy event to try and gain a few minutes of airtime and infect a few unprepared computer users," said a spokesperson for security firm McAfee.

The new virus, called Small.DAM, was spread through emails with a variety of subject lines purporting to be news. Other variants included "British Muslims Genocide" and "U.S. Secretary of State Condoleezza..."

The virus is a trojan - a program or message that look benign but contains malicious code - that is installed when a user opens the e-mail and clicks on an attachment. The attachment could be called Video.exe, Read More.exe, Full Clip.exe or Full Story.exe.

"When you click on the attachment it installs a backdoor on the infected PC giving full access to the virus writer to do anything they want," said Mr Hypponen.

"What they typically do is search your hard drive for credit card numbers and e-mail addresses because they can resell both of those."

Typically, said Mr Hypponen, the virus writers will then use the computer in a botnet - network of slave machines used to support all kinds of cyber crimes such as sending spam and phishing e-mails.

Users would not be aware that their computer was infected.

F-secure said it had seen "hundreds of thousands of emails sent" but did not know how many machines were infected.

"How many people clicked on it? It could be thousands or tens of thousands," said Mr Hypponen.

However, most firms treated the virus as a low security threat and have now issued security updates.