On move-in day his freshman year at St. Vincent College, Adam Zurawsky set up his computer and typed in a familiar Web address -- www.collegehumor.com.

But instead of being treated to the usual mix of racy images and offbeat articles, he got a blue screen indicating the site was off limits as potentially pornographic.

"I was in disbelief," he said.

Colleges are nothing if not defenders of free thought, and what young adults explore on their personal computers is usually their own business. But what if the setting is a Catholic campus and the material is sexually explicit?

Faced with that question shortly after taking office in 2006, St. Vincent President Jim Towey answered with a policy separating his college from many of its Catholic peers. His school, which has 1,900 students, filters out pornography sites from residence hall computers. Gambling sites are blocked, too.

Most of what's kept out of students' reach is far more extreme than the college humor site -- where photos of skin-baring models can be found along with less objectionable content. Mr. Towey said the proliferation of pornography, some hard core and violent, is degrading and potentially addictive to those who view it.

"I realize that we are in the minority of Catholic colleges and universities, but I like where we are," he said. "I think our Catholic identity and mission compel us to give this witness to our students that our community is not going to be complicit in this spreading of pornography."

Pornography sites are fertile ground for viruses, so any school that does not filter based on content can still block adult sites deemed a security threat. St. Vincent appears to go further by adding morality to the equation.

Mr. Towey, a former Cabinet-level administrator in the Bush administration, said he's received dozens of supportive comments. But in a recent campus blog defending his decision, he also noted he has critics, including someone who's been posting fliers anonymously on campus asking, "Is Mr. Towey our parent, or the college president?"

The filtering was implemented in August 2006 with no announcement, and some say they were unaware of it until late this fall when the fliers and Mr. Towey's blog appeared.

George Leiner, chair and associate professor of philosophy, said the college has a right to decide how its computer resources are used and to ask those insisting on more freedom to find other paths to the Internet. Still, he wishes the college hadn't acted, and he is unconvinced that students at St. Vincent are being led by computer into pornography or gambling addictions.

"I do think it has a chilling effect on the exploration young adults need to make as they are determining what positions to take on important matters in culture, whether they are academic, political, moral," he said.

Mr. Zurawsky, 19, a finance major from Greensburg, said he's more likely to look at gambling sites than porn. He said most students who attend St. Vincent are adults, adding it was shocking to him that something as innocuous as a humor site -- one he could view while still in high school -- is now considered inappropriate. "Who are they to tell us what we can and can't look at?"

Definitions of what constitutes pornography vary, as do estimates about the number of adult sites and how many people seek them out.

In one study, 38 percent of boys and 8 percent of girls ages 16 and 17 reported seeking online pornography in the past year, said Janis Wolak, research assistant professor with a University of New Hampshire center that studies Internet use and safety.

She said the respondents likely ranged from those who visited a site once or twice out of curiosity to those addicted.

At St. Vincent, the idea for filtering arose in July 2006, three weeks after Mr. Towey arrived from the White House, where he was assistant to President Bush and director of the Office of Faith-Based and Community Initiatives.

The school's dean of students at the time had circulated a memo to administrators noting computer misuse on the nation's campuses, particularly students' downloading of pornography. The memo sought Mr. Towey's authorization to use vendor-supplied software to filter out that material.

Mr. Towey said he weighed the moral and academic implications with campus monks, professors and administrators. One monk viewed the complex issue as a chance for St. Vincent to assert its Catholic identity in the modern age, while others "disagreed and felt that academic freedom required no Internet barriers," Mr. Towey said.

The system now in place on the campus network does not affect classroom computer labs, the library or faculty offices, nor does it apply to wireless hot spots. Students who believe legitimate sites are being blocked can appeal to have them white-listed.

Mr. Towey said he realizes those truly intent on finding explicit materials will find a way. The school's goal isn't to stop someone from viewing Sports Illustrated swimsuit photos.

"It's not like we're going room to room looking in people's drawers to see if they have a magazine,'' Mr. Towey said.

"I think academic freedom is an extremely important issue, but it's not an absolute," he said. "When you come to a Catholic college ... you have to look at the moral content of the education."

Still, a number of Catholic colleges contacted, including the University of Notre Dame and Boston College, said they do not filter pornography. Some said they opted against those restrictions, even though students caught downloading pornography could be in violation of computer-use policies and conduct codes.

"Informing students to be leaders means there has to be trust they will make appropriate judgments," said Boston College spokesman Jack Dunn.

The free flow of ideas, he added, is "central to a university environment."

Locally, La Roche College, Duquesne University, Seton Hill University, Carlow University and Wheeling Jesuit University all said they do not use pornography filters.

But Franciscan University of Steubenville does. The policy covers residence halls and certain public terminals, though computers in academic settings are generally exempt so legitimate research isn't hampered, said Max Bonilla, vice president for academic affairs.

He said institutions of higher learning, most fundamentally, are about bettering individuals and society. "Pornography is at odds with human dignity."