CDM  I had the same problem (macbook pro running leopard; internet cleanup 5.0). I booted from a clone to access the hard drive (alternatively you could access your HD in target mode from another mac). I then deleted everything I could find associated with internet cleanup. I deleted a bunch of .plist files, but I think the critical files to delete were netblockade.kext and/or netspywareblocker.kext (I might be misremembering that filename, but search for .kext files and you'll see the ones I mean). After that my machine booted; I downloaded the IC software again and chose the uninstall option. Things now seem to be back to normal.

Now to ask for my money back.  
(Version 5.0)

CHRISKT  My mac is freezing up too, can't get it to start at all. How do I bypass the screen with the stop symbol?  
(Version 5.0)