If your kaspersky antivirus 4 still has months [ or haven't expired yet] to go before to expiry, and you backdate your computer clock to 1 or 2 years backward, you will find the key will expire immediately, even though you set the computer clock to current date, and it won't remedy the expired key file. How to fix this problem? Reinstall the whole program won't help. Why is this happening? WARNING: don't try to backdate your computer if you are using kav 4. you will be regretted and finds the above happening.