I used Zone Alarm for many years and liked the simplicity of its configuration. Recently though it seems to have become much more intrusive doing things like installing unwanted toolbars in, for example, Outlook.
AVG I dropped a long time ago in favour of Avast, primarily because AVG was unable to find my internet connection and wouldn't update. However, even Avast seems to have become more bloated than it used to be and it does slow down the PC.
With Windows 7, I now use MSE, Windows own firewall, SpywareBlaster and Malwarebytes.
I can't help feeling that these previously good programs have been spoilt by trying to be too clever for their own good instead of sticking to what they used to do extremely well.
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Mike