Microsoft has re-issued a security patch, which was found to be ineffective just shortly after it was released on 10 June.
The patch was designed to address a remote code execution vulnerability in Windows XP and Vista which Microsoft had warned was a "critical" security risk.
But Microsoft soon had to take action as the patch was found out to fix the security issue in Vista but left XP vulnerable.
"As soon as we learned of that possibility, we mobilised our Software Security Incident Response Process (SSIRP) to investigate the issue", said Microsoft security and response communications lead Christopher Budd.
"Our investigation found that while the other security updates were providing protections for the issues discussed in the bulletin, the Windows XP SP2 and SP3 updates were not."
The updated version of the patch can be obtained automatically through the Windows Update and Microsoft Update services.
It can also be downloaded manually from the Microsoft Download Center website.