Consumers have been warned of the spread of a new worm.

MyDoom, also known as Mimail-R, spreads via email, using a variety of technical-sounding subject lines and attachment names.

If the attached file is launched and the worm activated, it scours hard disks for more email addresses to send itself to. MyDoom also opens a backdoor onto infected computers which allows hackers to gain access.

Unlike earlier worms, MyDoom does not attempt to entice users into opening attachments that promise pornography, gossip or prizes. Instead, it appears to be a 'test' email, and may bear the header "Status" in the subject line. Experts believe its apparent innocence may tempt some users to open it.

"MyDoom is unlike many other mass-mailing worms we have seen in the past, because it does not try to seduce users into opening the attachment by offering sexy pictures of celebrities or private messages," said Graham Cluley, senior technology consultant for Sophos.

"MyDoom can pose as a technical-sounding message, claiming that the email body has been put in a attached file. Of course, if you launch that file you are potentially putting your data and computer straight into the hands of hackers." It is thought that the worm is trying to seize control of millions of home and business computers around the world, in preparation for what is called a distributed denial of service (DDoS) attack against a company called SCO.

SCO is involved in legal arguments with companies that use the open source operating system Linux, and insists that it owns some of the code used in the software. The move has caused great controversy in the open source community.

In a DDoS attack, computers that have fallen into the hands of hackers through worms such as MyDoom are instructed to bombard a particular web address with requests for information. This can cause the target computer to break down under the weight of traffic sent to it, causing inconvenience for the company that owns it.

If such a message appears in your in-box, delete it immediately.