BBC News passes along the results of a study by Earthlink claiming that the average computer is “infested” with 28 spyware programs.
I have no idea of whether that number truly represents the average PC. In my experience, the number of spyware programs on a particular PC is either very low or very high. Security-conscious people have very little, whereas those who are unaware or ignorant of security threats tend to be targeted.
Two factors in particular seem to control how much spyware lands on a PC, as I see it: One is Kazaa, which opens the floodgates to a tidal wave of crapware and is, in my opinion, the single biggest threat to the PC ecosystem. The other is whether the owner of a particular PC pays attention to the need for security patches and updates. Without regular updates, it’s too easy for hostile software to sneak onto a computer.
On a related note, Dwight Silverman of the Houston Chronicle has published an excellent article that lays out his sensible five-step program for avoiding, detecting, and removing spyware. Bookmark it.
Ed Bott 
I agree with what you are saying. An “average” in this sort of area seems difficult to get as you do get the people who will accept any rubbish on thier computers- and others that lock them down and clean up /update all the time (I prefer the latter of course!)
A good friend of mine has had me wipe and re-install XP on his daughter’s computer twice in the last year.
The first time, a run of Ad-Aware found over 200 items it didn’t like. When I let Ad-Aware do it’s thing, it suddenly couldn’t find any site that required the use of a DNS server.
After several trips to the MS Knowledge Base, it was unrepairable as far as I was concerned.
The second time I used Spybot S&D and found over 400 nuggets on the machine. So I guess that there must be 14 clean machines out there to average out against hers.
Oh… both times she turned Norton AV off because “it slowed her machine down way too much.”