One of our employee reported me that his Skype is sending itself some dangerous links to his folks.
It occures that some unwanted addons was installed and enabled in his Skype installation. It also occures that other employees opened link retreived from "him" and now they have the same "addon" installed.
The fastest way to get rid of unwanted addons was to disable Skype API at all, by adding one entry to Windows registers.
Distribute this following entry with Group Preferences (Computer Configuration, not User Configuration). Once added to Group Policy, users' computers MUST be restarted while group policies are processed on Windows startup.