I use Malwarebites and Avast antivirus software, both free on the web.
They don't pick up everything but, with all the crap my kids get into online, I'm not surprised some stuff sneaks through, especially with the way
they constantly download games and crap onto that computer. I guess I'm just luck the desktop doesn't burst into flames.
Believe it or not, after replying to your thread, I too had a pop-up. It wasn't the same but was just as suspicious and had never happened before.
I noticed you're using Chrome. I too use Chrome. I read an article this morning stating that Chrome had just updated itself, and this allows the
makers of extensions, or chrome apps, to push their updates as well, and in the process may be able to hide malware in their updates. So it is
possible that a chrome extension is to blame, although I did receive the pop-up while on ATS. It might be reasonable to turn off extensions if the
problem continues.