While investigating the recently unearthed Flame (SkyWiper) toolkit, Microsoft's researchers have made an unwelcome discovery.

"We have discovered through our analysis that some components of the malware have been signed by certificates that allow software to appear as if it was produced by Microsoft," shared Mike Reavey, Senior Director, Microsoft Security Response Center.

"We identified that an older cryptography algorithm could be exploited and then be used to sign code as if it originated from Microsoft. Specifically, our Terminal Server Licensing Service, which allowed customers to authorize Remote Desktop services in their enterprise, used that older algorithm and provided certificates with the ability to sign code, thus permitting code to be signed as if it came from Microsoft."

The company released a security advisory detailing the issue and an update that revokes three signing certificates.

According to Reavey, the Terminal Server Licensing Service will longer issues certificates that would allow code to be signed.

Users are advised to apply the update as soon as possible.