Chrome Version 21.0.1180.57
On system launch every morning (but not on restarts or cold reboots), I get a full-screen popup system window with ads. In the upper-left corner is a logo that says "Sponsored Contents". The ads change every day.
BTW, the window appears to be generated at the OS level because it does not resemble the Chrome UI design. Closing it cancels it for the day; it returns on startup the next day.