New Delhi, Sept. 24 -- After deflecting the U.S. Justice Department's attack on its illegal monopoly in online search, Google is facing another attempt to dismantle its internet empire in a trial focused on its abusive tactics in digital advertising.

The trial that opened Monday in an Alexandria, Virginia, federal court revolves around the harmful conduct that resulted in U.S. District Judge Leonie Brinkema declaring parts of Google's digital advertising technology to be an illegal monopoly. The judge found that Google has been engaging in behavior that stifles competition to the detriment of online publishers that depend on the system for revenue.

Google and the Justice Department will spend the next two weeks in court presenting evide...