Well, I've run Spybot and Ad-Aware, and installed Firefox and Thunderbird, which are great.
Everything seems hunky-dory, no more pop ups, so many thanks to everyone.
I just looked at the thread title again and it struck me that it could have been taken as an attempt to warn people that Mudcat was responsible for what was happening.
If I gave that impression, I'm sorry and I certainly didn't mean to. I happily acknowledge that Max & co wouldn't dream of doing anything like that.