Apparently by mistake, Microsoft's Windows Server Update Services (WSUS) last night deployed a Skype update to Windows clients that had never had the telephony and messaging software installed. This resulted in Skype being installed on these computers.

The issue affects all computers that automatically receive Microsoft's updates via WSUS without explicit administrator approval. After the blunder surfaced publicly, Microsoft marked the update as expired. It is now no longer being deployed by WSUS servers.

Updates via WSUS are becoming increasingly popular in networks where multiple Windows systems need updating. With a WSUS server, administrators can minimize network loads and control which updates will be installed. In this case, the Skype update was deployed as a non-security update.