The flaw lies in the way Internet Explorer retrieves certain Cascading Style Sheet (CSS) objects, used to create a standardized layout on Web pages. For the attack to work, the hacker would have to lure a victim to a Web page that contained maliciously encoded JavaScript, Symantec said. This technique has emerged as a favorite way for hackers to install their malicious software on computers in recent years.

"To minimize the chances of being affected by this issue, Internet Explorer users should ensure their antivirus definitions are up to date, disable JavaScript and only visit Web sites they trust until fixes are available from Microsoft," Symantec said.