What is injecting commercials in my Google Chrome?

Question

When I browse Stack Exchange websites using Chrome, I see words highlighted in blue and double underlining, which popup a commercial page if I pass over the mouse (see picture).

This happens only when using Chrome. I could not find any related post on the Internet. Any idea on what is causing this problem?

(Note: Cookies are marked to be fully activated.)

Answer 1

I checked one by one my adds on, and the commercials went away when I disabled one called "FlashFree". The check was pretty quick, I browsed to chrome://extensions/, changed settings and tested by simply reloading (F5) one of the "polluted" pages.