For decades, marketers have waged a war against ad fraud and according to a new study, they just might win—or at least stop losing so much money.

Ad fraud occurs when purchased ads are displayed on sites that produce traffic artificially through bots, or when malware programs repeatedly “click” advertisements to simulate engagement. Obtaining sourced traffic—traffic acquired by a third party and therefore unverified—is also causing problems for marketers. A recent study by ANA found that 3.6 times as much ad fraud comes from sourced than non-sourced traffic.

By current estimates, brands will lose over $6.5 billion in 2017 due to invalid traffic (IVT) from bot fraud. This is a slight improvement over the estimated $7.2 billion lost in 2016, but the battle is far from over.

As perpetrators adapt to deterrents, any guarantee that marketing fraud will stop entirely is unrealistic. Partnering only with trustworthy advertising supply chains, however, may dramatically reduce invalid traffic.

A study conducted by The 614 Group tested the theory that using only TAG Certified channels would reduce or eliminate IVT when compared to the industry average.

Out of 6.5 billion impressions run through TAG Certified channels, just over 97 million impressions were identified as fraudulent. While that’s certainly a lot, the IVT rate was only 1.48 percent. This is a reduction of 83 percent compared to general industry and fraud rates.

Ad fraud continues to erode trust and budgets, but marketers aren’t going to take it anymore. Brands are banding together in solidarity to demand transparency and more control over how their marketing dollars are spent.

Founded by the ANA, 4A’s and IAB, The Trustworthy Accountability Group (TAG) whitelists companies as legitimate sources for digital ad impressions—a program joined by tech giants such as Google and Facebook. After a proprietary background check and review process powered by Dun & Bradstreet and subsequent approval by TAG, companies can be verified by name or by their unique, persistent TAG-IDs in a database.

In January, Proctor & Gamble announced that it would no longer buy media from companies who are not TAG registered.

“Walled gardens” that control most of the world’s advertising dollars in secret raise obvious concerns about transparency. To help put its clients at ease, Google joined the “Ads.txt” project through the Interactive Advertising Bureau in March. The new tool provides a mechanism to enable content owners to declare who is authorized to sell their inventory.

Google issued partial refunds to victims of ad fraud in August, vowing to develop a tool that provides more transparency for marketers. Together with companies like Twitter, Facebook and Microsoft, Google committed to meet “Gold Standards” set forth by IAB UK.

To combat ad fraud, TAG recommends that brands designate a trained Brand Safety Officer, communicate a clear and consistent policy for measuring ad fraud and work only with TAG Certified Against Fraud partners. The company also encourages brands to send a message by refusing to pay for ad fraud.

“Fraud thrives in the dark crevices of the supply chain, so we knew that we had to get the legitimate participants in the supply chain to adopt the same high standards for this effort to be successful,” said Mike Zanels, president and CEO of TAG in a statement. “When the industry links its arms and stands together, there is no place left for the criminals to hide.”