That's unusual. Do you have any kind of browser toolbars installed? Sometimes those can be ad-sponsored and perhaps they are getting past MBAM as legit programs. Like an ask.com or yahoo search bar or something.
If this is the first time you've seen it maybe check and re-install any programs you've added in the last couple days. During the install look carefully for that third party bundled software offer and uncheck that mo.
Aside from that maybe a quick swipe with Ad-Aware, but MBAM usually catches just about anything.