AFP - Microsoft on Wednesday released an emergency patch to fix a perilous software flaw allowing hackers to hijack Internet Explorer browsers and take over computers.

The US software giant said security update MS08-078 addresses a vulnerability cyber-criminals can exploit to their advantage.

"Microsoft encourages all IE customers to test and deploy this update as soon as possible," said Microsoft security response communications head Christopher Budd.

The threat posed by the IE flaw led Microsoft to mobilize security engineering teams worldwide to deliver a software cure "in the unprecedented time of eight days."

According to researchers at software security firm Trend Micro, attacks based on the vulnerability in the world's most popular Web browser were spreading "like wildfire" with millions of computers already compromised.

Microsoft typically releases patches for its software on the second Tuesday of each month and rushing this fix to computer users out-of-cycle is testimony to the severe danger of the threat, according to Trend Micro.

"When the patch is released people should run, not walk, to get it installed," said Trend Micro advanced threat researcher Paul Ferguson.

"This vulnerability is being actively exploited by cyber-criminals and getting worse every day."