Microsoft has confirmed that it is not just Internet Explorer 7 that is vulnerable to a new zero-day attack.

IE 5 and 6 have been confirmed as also vulnerable to the flaw which, when properly exploited, can allow a hacker to gain complete control of a vulnerable system.

"At this time, we are aware only of limited attacks that attempt to use this vulnerability against IE 7," said the company in a security advisory.

"Our investigation of these attacks so far has verified that they are not successful against customers who have applied the workarounds listed in this advisory. Additionally, there are mitigations that increase the difficulty of exploiting this vulnerability."

The flaw targets a component in IE7 that handles XML tags. When the page confirms that the user is running a vulnerable browser and operating system, a specially crafted tag is loaded.

"Any security vendor basing their detection rules on the publicly available exploits is not detecting attacks fully," said Carsten Eiram, chief security specialist at Secunia.

"Users should therefore not just browse around using IE thinking that they're safe. Setting the security level to 'high' for the 'internet' security zone will somewhat protect you. Combined with Microsoft's suggestions related to OLEDB32.DLL you should be able to keep your system to yourself."