Microsoft said on Tuesday that it is looking into reports of a new Windows flaw that could compromise the security of machines running older versions of the operating system.

In an advisory on its Web site, Secunia said that the vulnerability is due to a boundary error in a function included in Windows XP and Windows 2000 that, if exploited, could allow malicious code to be executed. The firm rated the vulnerability as "moderately critical."

"Microsoft is investigating new public claims of a possible vulnerability in Windows 2000 and Windows XP," group manager Jerry Bryant said in a statement. Bryant said Microsoft is unaware of any attempts so far to build an attack based on the vulnerability and included Microsoft's standard language that it will take appropriate action, which could include releasing an update as part of the company's monthly patches or issuing an unscheduled update.

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