Upon expiration of a commercial key file / activation code (such keys are valid for 1 year or more), the application keeps performing all its functions except updating antivirus databases.
It will be impossible to update antivirus databases from any source. In case of an attempt to manually download and add databases, the product ceases functioning at all.
Still Kaspersky Anti-Virus will keep curing infected objects/filtering spam using antivirus databases downloaded not later than the last day before license key expiry.
Using a commercial key file means a reject of trial key files making it impossible to extend the license period with a trial key file.
Upon expiration of a trial key file (such keys are valid for 1 month normally), the application stops functioning at all.
Installation of a trial key file makes it impossible to extend the license period with another trial key file. The second trial key file expiry date will be the same as that of the first one.
When application stops functioning upon expiry of a key file, its functionality can be restored simply by installing a new commercial key file issued for such application (or use a new activation code). There is no need to reinstall the application itself however.