This afternoon my computer keeps coming up with a message saying "This system is shutting down. please save all work in progress and log off. Any unsaved changes will be lost. This shutdown was initiated by NT Authority/System"
After searching on the net, it is clearly caused by some kind of virus. Aparantly it is causing lsass.exe to terminate, which then triggers the shutdown. A virus scan has not found any virus's, however one thing was identified, which said: