Further, in the last several years the Internet has seen a proliferation of “bum fight” videos, shot by young men and boys who are seen beating the homeless or who pay transients a few dollars to fight each other.

Indeed, the National Coalition for the Homeless, which works to change government policies and bring people off the streets, says in its new report that 58 percent of assailants implicated in attacks against the homeless in the last 10 years were teenagers.

Michael Stoops, the group’s executive director, said social prejudices were “dehumanizing” the homeless and condoning hostile treatment. He pointed to a blurb titled “Hunt the Homeless” in the current issue of Maxim, a popular men’s magazine. It spotlights a coming “hobo convention” in Iowa and says: “Kill one for fun. We’re 87 percent sure it’s legal.”

With victims wary of going to the police, statistics on the attacks are often incomplete. But surveys show much higher rates of assault, rape and other crimes of violence against the homeless than almost any other group, said Professor Levin, of California State, who worked on the new report.

Recognition of the problem is spurring legislative action.

“More and more, we’re hearing about homeless people being attacked for no other reason than that they’re homeless, and we’ve got to do something about it,” Representative Eddie Bernice Johnson, Democrat of Texas, said in an interview.

Image Matt OBrien, who advocates on behalf of the homeless, touring the flood channels. Flash floods may endanger those who stay there, he says, but at least they are safe from violence. Credit... Isaac Brekken for The New York Times

Ms. Johnson introduced a measure in the House last week to make attacks on the homeless a federal hate crime and require the F.B.I. to collect data on it. (The Senate voted last month to expand federal hate crimes to include attacks on gay and transgender victims, another frequent target.)