A new security vulnerability puts Windows users at risk of serious cyberattacks, Microsoft warned late Wednesday.

The vulnerability affects all recent Windows versions, including Vista, which Microsoft has promoted heavily for its security. The operating system software is flawed in the way it handles animated cursors, Microsoft said in a security advisory.

An attacker could exploit the vulnerability through a Web page or e-mail message with rigged computer code, Microsoft said.

"Upon viewing a Web page, previewing or reading a specially crafted message, or opening a specially crafted e-mail attachment, the attacker could cause the affected system to execute code," Microsoft said in its advisory.

Such holes are often exploited by cybercrooks to do "drive-by" installations of malicious software. Spyware and remote control tools that turn PCs into drones for the attacker are silently loaded onto vulnerable computers by tricking people to visit a rigged Web site or hacking a trusted site.

Sample code that demonstrates the vulnerability has already been posted on the Web, McAfee said in a security alert sent to customers. "Malware exploiting this vulnerability has been observed in the wild," the security company said in the alert.