If you are using Microsoft Internet Explorer (IE), there are hackers actively using a software bug to gain control of Microsoft Windows computers. Stop using IE now! This is twice as dangerous as the Heartbleed Bug because an attacker can take control of your computer and do whatever they want with it.
US-CERT issued an alert about the active exploitation of a use-after-free vulnerability in Microsoft Internet Explorer. This vulnerability affects IE versions 6 through 11 and allows a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system.
US-CERT recommends that users and administrators review Microsoft Security Advisory 2963983 for mitigation actions and workarounds. If you are still using Windows XP, Microsoft will not provide updates or solutions and you should consider installing and using an alternate browser such as Mozilla Firefox (free) or Google Chrome (free).