Circulation at U.S. newspapers fell in the six months through September while their online editions lured millions of readers, the Audit Bureau of Circulations said.

Print circulation at 609 daily newspapers dropped 2.6 percent to 40.7 million in the period from a year earlier, according to the ABC. Of those, 163 newspaper Web sites logged a total 164 million visitors monthly, it said.

For the first time, the ABC combined online readership with print circulation to create a measurement called "net combined audience" to show advertisers, investors and the general public that a newspaper's audience extends beyond its printed edition.