Microsoft has revealed that worms have undergone a resurgence in the first half of 2009, with infections doubling to rank the threat as the second most prevalent, up from fifth.
This was behind the miscellaneous trojans category, which remained the top threat category from six months ago.
This is according to the latest Microsoft security intelligence threat report, its twice-yearly findings from worldwide data taken from Bing, Windows Live Care and Defender, Forefront, as well as its Malicious Software Removal Tool (MSRT).
The number of worms had been falling in the first half of 2006 and 2007 but jumped back up by the end of 2008 and the first half of 2009.
Predictably, the Conficker worm was the biggest driver for this increase, coming as the number one malware software family detected by Microsoft.
Cliff Evans, head of security and privacy for Microsoft UK, said Conficker has had a "certain amount of success" in infecting machines.
"That's generated a lot of coverage, which is obviously picked up by criminals that who wanted something themselves," he said.
"They are about looking to make money out of this, so they are looking for the most effective method," he added.
The second biggest software family was a worm called Taterf, which targeted massively multiplayer online role-playing games (MMORPG). This increased by 156 per cent, from two million in the last report to 4.9 million in the latest one.
Although a worm targeting games may seem a consumer issue, Evans said that it could easily enter a enterprise network if employees were playing games in the workplace.
"Organisations should be making sure that they are protecting themselves in terms of thumb drives, making sure they are being scanned, and making sure malware was up to date," he said.
Evans said that it was difficult to know whether the worm trend would continue, but said it was more important that people took the right precautions to keep their computer secure.
