Laptop unusably slow with Internet Security 2012 switched on
I have a Sony Vaio laptop with Internet Security 2012 installed. Up until about 4 or 5 days ago it was working fine. Now the machine is unusably slow, and there is constant disk activity (but very low processor usage). If I turn Computer Security off it's fine again. Whilst it was off I checked for F-secure updates and one was installed. But the machine is still the same when I turn Computer Security on again.
Any ideas? Should I completely reinstall Internet Security?