Ad banners showing on Chrome

[jooch]

Hi, I know many of you have posted about ads and related stuff but i didnt find any similar problem.
When accessing to webpages like imdb, youtube, cuevana (a site for watching movies/series) and many other sites some weird banners appear and those are not the typical webpages banners, they show up in random places and have a big X to close the ad and it is really annoying. I read about blocking the cookies, javascript and pop ups but i cant get rid of 'em, I also tried scanning my computer with malwarebytes and running my antivirus scanner but they didnt find anything. Can someone please give me a solution, I dont think that the problem is the browser as it started happening like a week ago (an no, I havent installed anything or at least not that I noticed)

Examples of the ads:
IMDB: http://imageshack.us/photo/my-images/818/capturaads.jpg/
Cuevana: http://imageshack.us/photo/my-images/688/capturaads2.jpg/
Youtube: http://imageshack.us/photo/my-images/69/capturaads3.jpg/

Thanks in advance!

[tashi]

Hello jooch,

I dont think that the problem is the browser as it started happening like a week ago (an no, I havent installed anything or at least not that I noticed)

Any free extensions, apps or themes downloaded and installed from the Chrome Web Store?

http://www.computerworld.com/s/article/9227179/Wikipedia_warns_users_about_malware_injecting_ads_into_its_pages

Best regards.