Please refer to my post here:
http://www.theanswerbank.co.uk/Technology/Internet/Question1523879.html
Since I posted that, there have been further AB threads on the subject, suggesting that
(a) the 'free' program only searches for problems on your computer but then requires payment before it will get rid of them ;
(b) Scanguard doesn't do anything which the free version of Malwarebytes (which deserves a place on everyone's computer) can't do ; and
(c) after installing Scanguard, Malwarebytes actually detects PUPs (= 'potentially unwanted programs') which weren't there before. i.e.a program which claims to get rid of junk from your computer is actually putting it there!
As others have said, AVOID!!!