Harvard police yesterday warned students to be on the watch for a homeless man who might try to enter their dorms, and rooms, trying to befriend them.

Over the weekend, a homeless man conned students into letting him spend the night in Hollis Hall, prompting the warning.

The alleged con artist used the alias Seamus O'Reilly. Harvard University Police (HUPD) described O'Reilly as a 6-foot white male with brown hair, who spoke with an Irish accent.

The con started in early October, when the man approached a first-year in the Yard and identified himself as a first-year Harvard Law School student. The two chatted and ended up exchanging e-mail addresses.

O'Reilly said he was from a wealthy Irish family and owned an apartment on Beacon Hill. He said that his workload often prevented him from making the trip home.

Last week, Harvard police received reports of a man matching O'Reilly's description using computers in the Science Center without permission.

The first-year, who asked not to be identified, exchanged e-mails with O'Reilly over the course of a week. One day, when the student returned to her room, O'Reilly was outside. She invited him up, and he ended up taking a nap for several hours.

"It was somewhat of a flim-flam," said HUPD spokesperson Peggy A. McNamara.