Updated: Justice Department Investigating Yahoo-Google Ad Test; Companies Say They Volunteered Info

The U.S. Department of Justice is looking at the Google-Yahoo (NSDQ: YHOO) two-week ad test, according to Reuters. The wire service says it has been told by a source that authorities have initiated an investigation over concerns the test could violate antitrust law.

The test, announced early this month, was limited to two weeks, U.S. searches of Yahoo.com and just 3 percent of search queries.

Update: The companies have confirmed communications with the DOJ. A Google (NSDQ: GOOG) spokesman told Reuters: “We informed the Justice Department before we launched this test and we have been responsive to their questions about it.” Separately, a Yahoo spokesman said the company has pro-actively kept the DOJ in the loop.