Microsoft has warned that every version of Internet Explorer is vulnerable to a major attack Relevant Products/Services that could provide hackers with complete access to a computer. The vulnerability, which affects versions six through 11 of the browser, is particularly bad for Windows XP users since they won't be receiving the fix.

There are multiple browsers that people use, including Chrome, Firefox, and Opera, but Internet Explorer remains the most popular. The vulnerable versions of the browsers account for 55 percent of the total market.

Detailed information regarding the issue has yet to be provided by Microsoft, though FireEye, the group that discovered the vulnerability, has been tracking the flaw's exploitation. According to its report, at least one group of hackers has been exploiting the flaw, though there could be others.

Operation Clandestine Fox

The Internet Explorer flaw is a "zero-day" threat Relevant Products/Services, which means that hackers began to take advantage of it before Microsoft learned of its existence. Some vulnerabilities are discovered and fixed before anyone can exploit them, but in this case, at least one group has already been using it.

FireEye said that it has discovered one campaign, called Operation Clandestine Fox, that is actively relying on the Internet Explorer flaw. The operation appears to target the U.S. military and other major organizations. FireEye told Reuters that the group seems to be gathering "intel," though it will not release any additional information.

Given its knowledge regarding the way hackers are using the flaw, FireEye says that around one-quarter of the "total browser market" is actually at risk. Although 55 percent of computers are running the affected versions of Internet Explorer, FireEye says that only versions 9 and above have been targeted.

XP Users Out of Luck

Since Microsoft discontinued its support for Windows XP, many have predicted that significant security Relevant Products/Services issues would arise. Microsoft cut off support just a few weeks ago on April 8, and already the first un-patched flaw has already reared its head.

As Windows XP was losing its support earlier this month, Microsoft updated its information center to let users know how a lack of support actually affects them. In the Windows lifestyle fact sheet, Microsoft clarifies that a version of Windows that is not receiving support will no longer get security updates. This means that many of the businesses still using XP won't be safe if they are also using Internet Explorer.

"An unsupported version of Windows will no longer receive software updates from Windows Update. These include security updates that can help protect Relevant Products/Services your PC from harmful viruses, spyware, and other malicious software, which can steal your personal information," according to Microsoft.

Businesses and individuals that have upgraded to a more recent version of Windows will still be vulnerable until a patch is provided by Microsoft. FireEye says that people should either switch to a different browser in the meantime or disable Adobe Flash, which will protect them from an attack.