Microsoft is releasing a patch on Monday for older versions of its Internet Explorer browser, deviating from its normal repair schedule due to the seriousness of the problem.

The vulnerability, which is present in IE 6, 7, and 8, is a memory corruption issue. It can be exploited by an attacker via a drive-by download, a term for loading a website with attack code that delivers malware to a victim's computer if the person merely visits the website.

Microsoft released a quick fix for the issue earlier this month, but did not have a more permanent patch ready when it released its monthly batch of patches last Tuesday. The company will occasionally release an emergency patch if the software vulnerability is considered a high risk.

"While we have still seen only a limited number of customers affected by the issue, the potential exists that more customers could be affected in the future," wrote Dustin Childs, group manager for the company's Trustworthy Computing Group, on a company blog on Sunday.

The patch, which will be released at 10 a.m. PST, will be distributed through Windows Update. Childs wrote users will not have to uninstall the quick fix before applying the patch, which will be installed automatically for those who have automatic updates enabled.