Microsoft Admits to Huge Security Flaw in Internet Explorer

A flaw in Microsoft’s Internet Explorer web browser could allow hackers access to the personal information of countless millions of web users, especially those still using Windows XP.

On Sunday, the company warned of a glitch in versions 6 to 11 of Internet Explorer that potentially give data thieves using a network computer the same level of access as the legitimate user.

Admitting to being aware of “limited, targeted attacks that attempt to exploit a vulnerability,” Microsoft explained that the “vulnerability exists in the way that Internet Explorer accesses an object in memory that has been deleted or has not been properly allocated.”

Internet Explorer’s market share has dropped precipitously over the past decade, but it remains the browser of choice for around 10% of netizens — behind Google Chrome and Mozilla Firefox.

The bug’s disclosure comes in the wake of Microsoft’s much publicized decision to stop supporting the Windows XP operating system.

“XP users are not safe anymore, and this is the first vulnerability that will be not patched for their system,” Internet security firm Symantec Corp. researcher Christian Tripputi wrote in a blog post.

MORE: Internet Explorer Security Flaw: 4 Ways to Protect Yourself

Write to Charlie Campbell at charlie.campbell@time.com.