Not sure if this is a bug or not (though it seems possible).
I update the virus database and after it reported finished I disconnected from the internet and went off
to do something else. I came back about 4 hours later and there was a baloon message saying that it failed
to update the virus database. I dismissed it and went to bed.
The next day I saw the baloon message again. I activated my DSL connection and tried updating the virus database but the program reported I was already up to date. I disconnected my DSL and an hour later I got the baloon message again.
It seems that CIS expects you to be always connected and reports failure messages if you’re not.