This actually started some months ago on both my PC's at pretty much the same time. I use Avira as AV. For some reason though it just wouldn't update anymore. Normal the updater gets to about 250kb, waits half a minute then does another 250kb, waits half a minute... etc. Somewhere between 1 and 1,5MB into the update it just stops and a few minutes later it shuts itself off.
About two months ago I did a complete reinstall on my one PC. Used AVG for a while and that worked fine but I thought I'd try Avira again, downloaded the latest version but it still won't update.
I started a thread about this at the Avira support forum: Cannot update Avira - Avira Free Antivirus für Windows - Avira Support Forum
but was wondering if anyone here had any suggestions...