Google defends its ad business in court, claiming a breakup would be complicated and disruptive. The DOJ argues for structural changes to prevent monopolistic practices. The judge shows mixed responses regarding necessary remedies.
Google defends ad tech monopoly
DOJ pushes for structural remedies
Judge's signals are unclear
Experts cite technical complexities
Google offers limited concessions
Concerns about future monopolistic practices
The U.S. Department of Justice and 17 states have asked a federal court in Virginia to force Google to sell its advertising exchange (AdX) and to open source its publisher ad server software (DFP). In April 2025, Judge Leonie Brinkema ruled that Google holds illegal monopolies in display ad auctions and publisher ad servers. The remedies trial began in late September 2025.[1][2]
Case Background and Market Control Details
The DOJ’s complaint cites that Google controls 56 percent of open-web display auctions through AdX and 91 percent of publisher ad servers via DoubleClick for Publishers. The proposed remedy would divest AdX and require Google to release DFP’s auction logic under an open-source license. If competition does not improve within four years, the DOJ may seek a full sale of DFP.[2][3]
Technical Complexity of System Separation
Google engineers testified that AdX and DFP share a single codebase of approximately 35 million lines, supported by about 300 engineers. Engineering Director Glenn Berntson described the task of separating these systems as “massive,” noting deep interdependencies across infrastructure and services. Columbia University computer scientist Jason Nieh estimated it could take at least five years to replicate Google’s proprietary features outside the company.[3]
Security and Fraud Risks of Divestiture
Google warns that divesting AdX from its integrated security framework would expose the exchange to heightened cyber threats. Vice President Heather Adkins testified that without Google’s defenses, a standalone AdX could become a target for coordinated attacks. Engineers also cautioned that built-in fraud detection signals would be lost, potentially increasing ad fraud and harming publisher revenue.[3]
Key concerns raised during testimony include:
Exposure to coordinated cyberattacks without integrated security
Loss of built-in fraud detection capabilities
Increased risk of ad fraud targeting publishers
Potential revenue harm from fraudulent transactions
Market Impact and Transition Challenges
Mergers and acquisitions expert Shane Goodwin highlighted that legal veto rights for buyers and the need for global regulatory approvals could delay or derail any sale. Publishers fear operational disruption and revenue volatility during the transition. Smaller publishers that depend on Google’s free ad server might face new costs or reduced technical support.[4]
Competing Arguments on Divestiture
The DOJ contends that a divestiture is essential to restore competition in ad tech. Google and its experts maintain that unwinding its ad tech stack poses severe technical, security, and market risks that could take years to resolve. The court’s ruling will determine the future structure of open-web advertising.
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Verified all market-share and trial data with DOJ filings and reports.
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— by Howayda Sayed
Verify market-share data regularly with reports from eMarketer and IDC to ensure figures remain current.
Reference official court filings for rulings and trial timelines to maintain precision.
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FAQ
Who are the main competitors Google might face if its ad tech operations are divested or open-sourced?
The Trade Desk and Magnite operate ad exchanges, while OpenX and Prebid (used by 31% of top 1M websites) provide publisher ad server alternatives. However, these platforms remain significantly smaller than Google's 91% market share in publisher ad servers.
What specific technical challenges would Google face in actually separating AdX from DFP given their shared infrastructure?
AdX and DFP share 35 million lines of code supported by 300 engineers with deep interdependencies. Columbia University computer scientist Jason Nieh estimated it could take at least five years to replicate Google's proprietary features, with separation complicated by shared security frameworks and fraud detection systems.
How might publishers of different sizes be affected differently by these remedies?
Large publishers can transition to alternatives like Prebid or OpenX—header bidding adoption has driven 25% ad revenue growth for some publishers. Smaller publishers relying on Google's free ad server could face significant transition costs and reduced technical support without substantial new investment.
Why is cybersecurity such a critical concern for a standalone AdX, and what could advertisers and publishers lose?
A standalone AdX would lose Google's integrated security defenses and built-in fraud detection, increasing vulnerability to attacks and ad fraud. This could raise costs through higher fees, lower publisher payouts, or require additional third-party fraud detection investments.
How do global regulatory considerations complicate the divestiture process?
Buyers must secure regulatory approval across the U.S., EU, UK, and other jurisdictions with different antitrust standards. Coordinating multiple regulatory reviews historically extends timelines by months to years, as demonstrated by the HPE-Juniper divestiture.
When can publishers and advertisers expect to see concrete changes if the court orders are implemented?
A timeline depends on Judge Brinkema's remedies ruling, not yet announced. Historical antitrust divestitures suggest 12-18 months for planning plus additional months for global regulatory approvals, meaning substantive changes would likely occur no earlier than 2026.
