Since I uninstalled Windows Defender everything runs smoothly. At that time, when running msconfig to check what programs were launched at startup, I also cleaned some other stuff:
Adobe Reader Speed LauncherISUSScheduler (InstallShield, probably update checker)NeroFilterCheckPCSuiteTrayApplication (Nokia mobile phone connection, I now run whenever I need it)QuickTime Task (another update checker, I think)TkBellExe (another update checker, now from RealNetworks)
Just one odd behaviour is still around:
When an update is found and downloaded on one PC, sometimes it doesn't run on the other 2, not even if I do the manual update.Could it be there's different servers where they search the updates, or something else?