Looking at my IPSDefs folder on my machine, I can see definitions from
I once asked about this and the response that I got was that this was caused by Internet Explorer locking the definition files when LiveUpdate was trying to update them. I was also told that the old definitions would be deleted the next time the definitions were updated after the machine rebooted.
Well this doesn't seem to be working correctly in NIS 16.5.0.135.
The following IPSDefs defintions are on my machine:
20090420.001
20090427.003
20090501.001
20090508.002
I know I've restarted my machine a few times after April 27th and before May 8th so the April definitions, at least, should not be there, yet they still are. I had to manually remove them (and update the usage.dat file and the registry) to get rid of them.
The VirusDefs and WebProtectionDefs don't have a problem with old definitions sticking around, only the IPSDefs