Have you loaded the latest Microsoft security update for Windows? You might want to uninstall it because there’s a rising tide of complaints that it can shut down PCs with no warning. The screen just goes blank and with it goes anything you – or your students or teachers—have been working on. It’s the November 10-th update that is to blame because it changes the computer’s Access Control List of approved users. The best fix so far involves editing the registry file, but comes not from Microsoft, but Prevk, an English security firm.