QUOTE(Air Jordan @ 14.05.2009 21:16)

key is for 20 computers. For example we installed OS and used key to activate KAV on PC no.1 on 20/01/09, expiry date shows as 20/01/10, PC no.2 installed and KAV activated on 25/01/09, expiry date on that PC shows as 25/01/10. If we used 12 activations and have 8 activations left, and want to reinstall OS on PC no.1 today, what should be done, so it shows expiry date as before - 20/01/10, and not to use 13th activation and set expiry date to 14/05/10. It's a bit confusing, but I hope you will understand.
What confuses me is that each PC has it's own KAV license expiry date, which is in contrast with your reply. It is purely dependant on date of activation on that particular PC.
I may tell you, how the expiration is working in germany. I think it's similar to how it's working in other countries, too.
On creation of the license there is a expiration date like Vitaly already stated. But in most cases there is accommodation period for customer to activate some clients later without loosing licensetime on that clients. Just an example:
If the accommodiation period is two month and the key was created on 1st mar 2009 and you install some PCs on 10th mar 2009, they will expire on 10th mar 2010. If you install some further clients on 14th apr 2009 they will expire on 14th apr 2010. But if you activate further clients on 25th jun 2009 they'll expire on the max expiration date due to those two month period which would be 30th apr 2010.