Hi,
If you fire up a good search engine, but get no info on the file concerned, then it may indicate the presence of undesirable elements on your machine. An HiJackThis scan and a post on the malware removal forum is then usually indicated so that an expert can analyse your whole log and give you specific advice.
Having said that, the cjstm50.exe is usually associated with Canon Printer driver software, so if you have ever had a Canon printer attached to your machine., this may provide a route for further enquiry.
Regards
paws
Thanks a lot, paws, you have put your finger (?!) on it: There is a Canon printer running off this machine, so that is it. I am happy it was nothing serious.