Microsoft warned Windows users of three critical flaws in its software and urged them to install patches.
The security holes affect the way Windows handles certain graphic files.
If left unplugged, they could allow hackers and virus writers to take control of personal computers remotely.
Users of Windows XP, Windows Server and an updated version of Windows 2000 are advised to install a patch, which can be downloaded from the Microsoft website.
Two of them could potentially allow a hacker or virus writer to gain control over a Windows PC, and security experts believe they may be exploited.
"It wouldn't surprise me if this didn't get the interest of the hacker community," said Graham Cluley, senior technology consultant at net security firm Sophos.
"It is interesting because a hacker could either direct someone to a website containing one of these graphics or send an HTML e-mail containing one and that would be enough," he said.
