Howdy folks (BigTex inside joke)
etresoft's EtreCheck is mission critical at this point for us to be able to see what is "under the hood" of your Macs
BUT
the fact that this happens on BOTH Macs brings this question to my mind:
" are these MacKeeper popUP/UNDERs happening on ALL pages visited OR just one (or a select few)? "
Also, what specific "action" by you triggers the misbehavior? Click anywhere at all on a page of the website?
If yes, this is either by design of the site owner OR the site has been hacked.
I have used Firefox browser for a long time. It has an add-on available (only FF, as far as I can determine) that is an effective killer of these critters (requiring manual updating of a local 'blacklist' - but it's easy)
P.U.K a rude PopUp/Under Killer :: Add-ons for Firefox
Maybe some other fine folks that use other browsers habitually will know of similar add-on extensions of their favoeite browsers