security researchers in the U.K. have now published "proof of concept"
code for unpatched bug in the way Microsoft Internet Explorer browser
handles the JavaScript computer language.
It shows how hackers could exploit the problem and possibly
take over a Windows system.

According to Russ Cooper, this vulnerability has been around since May.
the malicious code can be launched by just one simple click on a Web link.

All users of Internet Explorer version 5.5 and 6.x are affected by the vulnerability

you may turn off JavaScript in Internet Explorer's Internet Options menu, or to use an alternative browser like Firefox or Opera to avoid this problem.

http://www.infoworld.com/article/05/11/21/HNiebug_1.html