The AVG program regularly updates its virus database.
My apparently up to date AVG on this computer currently has virus database 4031.1.1/7967, downloaded just short of 6 hours ago.
My laptop is showing 4189/8464, 21 hours old.
Additionally the AVG program itself is occasionally replaced completely. This is an update of the program itself, rather than the virus database. The program updated on one of my computers a week or so ago. Different computers are invited to update at different times within, as far as I can tell, a period of a week or so, presumably so they don't all hammer the servers at once.
On this computer, which has not updated recently, I have AVG version 9.0.932.
My laptop, which recently updated, requiring a reboot, shows AVG version 2015.0.5315
This probably explains the very different virus database version numbers and I shall prod AVG to see if it wants to update here...
... AVG prodded, no change.