Facebook on Wednesday banned ads on its flagship website and Instagram photo and video sharing service that claim widespread voting fraud, suggest U.S. election results would be invalid, or which attack any method of voting.

Russian actors believed to be connected to the government have been involved in spreading divisive content and promoting extreme themes in the run-up to the U.S. midterm elections. But they are working harder to hide their tracks, according to government investigators, academics and security firms.

Yahoo Inc. last year secretly built a custom software program to search all of its customers' incoming emails for specific information provided by U.S. intelligence officials, according to people familiar with the matter.