Microsoft was scrambling Sunday to repair a security hole in its widely used Internet Explorer web browser, saying it had detected attempts to exploit the flaw. The flaw affects Internet Explorer versions 6 through 11.These versions dominate desktop browsing, accounting for 55 percent of the PC browser market, because Microsoft stopped supporting the 13-year-old operating system earlier this month, reports, Agence France-Presse (AFP).

Earlier this month, the “Heartbleed” flaw in Internet security saw everyone from website operators and bank officials to casual Internet surfers and governments being told their data could be in danger.

The Heartbleed bug seems focused on user data and hackers, it’s also possible that the server could extract personal user data from any client.

Cybersecurity firm FireEye, which took credit for identifying the flaw, said hackers were exploiting the bug in a campaign nicknamed "Operation Clandestine Fox."

The vulnerability was reported to Microsoft by research firm FireEye. FireEye says that, while the vulnerability affects all versions of IE, the attack is specific to versions 9, 10 and 11. It is a "use after free" attack in which memory objects in the browser are manipulated after being released. The attack bypasses both DEP (Data Execution Prevention) and ASLR (Address Space Layout Randomization).

                               

While all versions of IE contain the vulnerability, security vendor FireEye, which initially reported the flaw, has only seen IE 9 to 11 being attacked. According to the company, the attackers are using a “well-known Flash exploitation technique” to gain access to memory and bypass Microsoft’s built-in anti-exploit technologies.

The company said, IE users to download and install its Enhanced Mitigation Experience Toolkit (EMET), a free tool that can help strengthen security on Windows. EMET must be version 4.1 or higher to prevent an attack using this flaw.

This is the first major vulnerability since Microsoft stopped support of Windows XP on April 8, supporting the older operating system with security patches and other software updates.