Those programs will only mess up your comp if you delete stuff that you shouldn't. That's why after scaning your comp they show the results and offer you a chance to choose what to delete and what to not.

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iMac G4 OSX 10.3.9
RAM 256MB
LW 4.10.5 Basic
ADSL anything from 3 to 8Mbps/around 1024kbps

"Raise your can of Beer on high
And seal your fate forever
Our best years have passed us by
The Golden Age Of Leather"
-Blue Öyster Cult-