SAN FRANCISCO (CNNMoney) -- Google is no stranger to federal investigations of its ever-expanding empire. Here's a new one to add to the list: Google has set aside $500 million for a potential settlement with the U.S. Department of Justice regarding the company's advertising practices.
The news, slipped Tuesday into a regulatory filing, caught many by surprise. The filing appears to be the first time Google has disclosed the DOJ probe. It offered few details, saying only that the DOJ has been investigating "the use of Google advertising by certain advertisers."
The company has not yet settled, and declined to comment further on the nature of the investigation or the timing of any potential settlement.
At Google's (GOOG, Fortune 500) annual I/O developers conference in San Francisco, co-founder Sergey Brin dodged questions about the filing.
"Luckily, since we changed roles a few months ago, I don't have to deal with filings, and the DOJ, the SEC or other acronyms," Brin said.
When Larry Page took the reins as CEO from Eric Schmidt last month, Brin lost his "Google president" title and now focuses exclusively on engineering.
After setting aside the $500 million, Google said it revised its profit down for the past quarter, which ended March 31, 2011. It said it earned $1.8 billion, or $5.51 per share, down from the $2.3 billion, or $7.04 per share that it initially reported last month. The net income that Google initially reported already fell short of Wall Street's estimates.
The company said it does not expect that any significant financial hit from a potential settlement.
"Although we cannot predict the ultimate outcome of this matter, we believe it will not have a material adverse effect on our business, consolidated financial position, results of operations, or cash flows," Google said in its filing.
Google is becoming a favorite target for government watchdogs. The European Union is currently investigating Google for possible antitrust violations, and the DOJ heavily scrutinized the company's recent purchase of flight data software company ITA. 
