My Spybot-scan found a PUPSC-threat in a (freeware) program called RegCleaner. This is the additional information:

Company:
Product: RegCleaner
Threat: PUPSC

Functionality:
supposed to speed up system performance by cleaning the registry

Description:
The sense for udage of registry cleaners is doubtful since the speed up effect of these tools is usually not present. Some registry cleaners can be used on user preference as long as those are free of cost. It is not recommended to pay for software which cannot prove its usefullness.

Doesn't seem a threat to me. Can anybody tell me what this means and why Spybot tells me this is a threat?

I use Spybot 1.6 and updated the latest definitions.