Thank you DennisD,
There is nothing related to it in the task scheduler. Don't know what to think now.
Yes I've experienced infuriatingly undisciplined software too.
I had elected to follow this thread but it didn't happen.
Edit: I had another look in task scheduler and found it under a confusing name. I've disabled it.
Edit 2: It still started. I then deleted the task from the scheduler but the damned thing still starts. I will ask Ashampoo to see if they can help.
Solved: It's not CCleaner's fault, neither is it task scheduler's. I'm embarassed to say that it's mine.
I had missed the fact that there is a checked box which lets it start at boot.