Microsoft will release 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.