Adblock Plus, a popular extension used on Chrome and Firefox browsers, is supposed to block pop-up ads, but it is now being reported that Google and others have paid Adblock Plus not to block their advertisements.

The German news site reported that Google and other unidentified companies paid Eyeo, the company that owns Adblock Plus, to be on a special "whitelist."

Eyeo and Google were contacted by the about the report on Friday, but have not yet responded.

The FAQ page on the states: "We have to add filters to allow ads that aren't intrusive, this cannot be an automatic process. However, this is far from trivial — the same advertising network might serve non-intrusive advertisements on some web sites and intrusive advertisements on others."

"Whitelisting is free for all small websites and blogs. However, managing this list requires significant effort on our side and this task cannot be completely taken over by volunteers as it happens with common filter lists. That's why we are being paid by some larger properties that serve nonintrusive advertisements that want to participate in the Acceptable Ads initiative. "