Google may have paid Adblock Plus to whitelist its ads, allowing the company's paid search results to appear even when the ad-eliminating browser extension is installed.

This whitelisting practice happens by default for Google and other unnamed companies who have funded Adblock Plus, according to German-language news site Horizont Online.

However, not all ad-dependent websites are a part of this special "Acceptable Ads" club.

Since Adblock Plus is one of the top software add-ons for Google Chrome and Mozilla Firefox, this has a significant impact on the revenue of banner-filled websites.

Acceptable Ads policy

Adblock Plus' goal is to eliminate annoying video ads, according to its parent company Eyeo.

It defends the whitelisting practice, according to Salon, pointing out that "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."

Which large companies pay to skirt the ad-blocking software remains a mystery, as does the parent company's criteria for determining small websites and large websites that have to pay.

TechRadar contacted Google for further clarification on the matter, while Eyeo's websites are currently down. We will update this story upon hearing back.