Forty percent of the largest 500 U.S. companies have disciplined employees over Internet porn and other illicit images in the last 12 months, a market research firm said Monday.

In addition, of those U.S. firms that pursued an investigation into illicit images, some 44 percent fired employees involved in the incidents, and 41 percent took some other disciplinary action, according to Delta Consulting's 2005 Computer Usage Policy Study.

The rate of disciplinary action, however, was far less than in the United Kingdom, where a recent third-party survey found that 70 percent of companies had taken porn-related disciplinary actions against workers, Delta said.

In the U.S., 1 in 4 managers lacked awareness of legislation linked to porn prevention in the workplace, and almost half were not fully aware that attorneys first look for evidence in sexual harassment, workplace harassment and hostile work environment claims in a companys records of Internet use, e-mail traffic and images on the hard drive.

In addition, 3 in 4 U.S. companies were not fully aware that the distribution and consumption of child porn is one of the FBIs top three investigative priorities for the next two years, Delta said.