Complex sentence: Returnil can be useful in preventing virus and spyware programs from making permanent changes to the system partition, they can still infect the system and cause stability/security problems on the PC until the computer is rebooted and restored to a state before infection.
Split into simpler sentences: Returnil can be useful in preventing unwanted programs from making permanent changes to the system partition. However, they can still infect the system and cause stability/security problems on the PC until the computer is rebooted and restored to a state before infection.