Many thanks, guys! As I always and only download direct from Piriform, I went with MTA and the problem is resolved. Good job, too - the amount of clutter I'd accumulated!
Running up-to-date AVG Internet Security 2015 and latest CCleaner Since the last CCleaner update and/or the latest AVG IS update, AVG insists that ccleaner.exe is an unknown threat.
Does anyone else have experience of this? Worked out what to do?