Kaspersky Lab products are installed with the Antivirus package driver. It is necessary to reboot the system for the driver to start functioning. If you do not reboot your PC after installation, the anti-virus components may work incorrectly (the only exceptions are on-demand scan and update module of the antivirus database)
It is recommended to reboot your PC after the application upgrade or hotfix installation as during this procedure some program modules and application drivers are changed by the upgraded ones.