Shoutbox

The sponsor program of Messenger Plus! is indeed the least intrusive and contains the least "stuff" of all the sponsor programs from LOP. It also does NOT contain any adult related materials. This is one of the major points which Patchou demanded from the sponsor program.

All the things you said considered, it indicates that the adware you're talking about is not from Messenger Plus!' sponsor at all. Mind you that there are thousands of other stuff your children can install which include truely hidden stuff and it even might not be visible that it is installed. Even browsing with a bad protected or set-up browser can cause harmfull things to be installed... (eg: clicking on certain popups which look like real security warning popups, can cause things to be installed on your computer).