A federal judge ruled Thursday that Alphabet's Google illegally maintained monopolies in two online advertising technology markets. The decision by U.S. District Judge Leonie Brinkema found Google liable for "willfully acquiring and maintaining monopoly power" in the markets for publisher ad servers and ad exchanges.

The ruling represents a significant victory for the U.S. Department of Justice and a coalition of states that brought the case against the tech giant. Judge Brinkema determined Google monopolized publisher ad servers, which websites use to store and manage ad inventory, as well as ad exchanges that connect buyers and sellers.

The court rejected a third claim that Google monopolized advertiser ad networks. This partial victory prompted Google's vice president of Regulatory Affairs, Lee-Anne Mulholland, to announce the company will appeal the ruling against its publisher tools.

"We won half of this case and we will appeal the other half," Mulholland stated. "Publishers have many options and they choose Google because our ad tech tools are simple, affordable and effective." Following the news, Google shares fell approximately 2.1% in midday trading.

The ruling comes as Google recently announced its largest-ever acquisition - a $32 billion all-cash deal to purchase cybersecurity company Wiz. The acquisition aims to strengthen Google Cloud's security offerings while allowing Wiz to continue serving competitors like Amazon Web Services and Microsoft Azure.

The decision opens the door for the Department of Justice to seek significant remedies in a future hearing. Antitrust prosecutors may pursue a breakup of Google's advertising technology business, potentially forcing the company to sell off its Google Ad Manager, which includes both the publisher ad server and ad exchange components.

This case adds to Google's regulatory challenges. Next week, a judge in Washington will conduct a trial on the DOJ's request to make Google sell its Chrome browser and take other measures to end what prosecutors claim is its dominance in online search.

During the three-week trial last year, prosecutors argued Google built its monopoly by acquiring competitors, locking in customers, and controlling online ad market transactions. Google's defense claimed the case focused on past behavior while ignoring competition from companies like Amazon and Comcast as digital ad spending shifted to apps and streaming video.