Stanford University officials, for the second time this week, found themselves Friday dealing with an interloper who has managed to pass herself off as a member of the university community for months.

The latest incident involves a woman, identified as Elizabeth Okazaki, who essentially made herself at home in the campus' Varian Physics Laboratory, sometimes spending the night there, using the computers and attending seminars, according to students.

University officials say they are taking steps to keep Okazaki off campus. Some students say the situation has been going on since at least 2004.

"I thought she was just another grad student, but then you talk to her and you realize that perhaps she doesn't really know what's going on," said Surjeet Rajendran, 24, a graduate student in physics. "She pretended to know physics, but it was very obvious that she didn't have any idea what she was talking about."

Okazaki alternately said she was affiliated with another academic department, was working on an ambiguous project that combined physics with humanities, or was working with renowned physics Professor Leonard Susskind, one of the leading contributors to the string theory concept, students said.

Susskind, in an e-mail, said he knew very little about Okazaki, and she had never worked with or for him.

How Okazaki came to frequent the physics lab is unclear. Several students said they had heard she used to work for the department years ago, perhaps as a temporary clerical worker. A university spokeswoman said she could not comment on whether Okazaki had been a university employee.

Whatever the reason, the largely nonconfrontational atmosphere in the physics department allowed her to go unchallenged for years, some students said.

"A university has a lot of weird people," Rajendran said. "Some of the faculty are weird, some of the grad students are weird. So you don't really know who's who. And you feel rather, I guess, rude asking them, 'What the hell are you doing?' I guess in that way it helps some strange people hang out without too many questions being raised."

Undergraduate physics student Brendan Wells, 22, said Okazaki is harmless.

"A lot of what she does is just use the computers, make tea and just kind of use the space as a place to be," said Wells. "I don't know if that's because she doesn't have somewhere else to go or she prefers it here."

Wells said he last saw Okazaki in the physics building Friday morning. She could not be reached for comment later in the day.

University attorneys are preparing a letter notifying Okazaki that she is not allowed on campus while police and university officials investigate her actions, Stanford spokeswoman Kate Chesley said.

"Stanford is a private institution," Chesley said. "We have the legal right to bar anyone from the premises, including people we reasonably believe will disrupt or have disrupted operations."

The emergence of Okazaki comes on the heels of revelations earlier this week that an 18-year-old Orange County woman, Azia Kim, had passed herself off as a freshman for most of the school year, convincing students to let her room with them in two separate dorms for about eight months.

Vice Provost for Student Affairs Greg Boardman said the university is launching a sweeping investigation into the Kim case, including "seeking to discover where there may be gaps in Stanford's system of identifying enrolled students."

Both cases are being investigated by Stanford police and campus officials.

"We consider this very serious," Chesley said. She added, however, that Okazaki's situation was different from the young woman who lived in university housing as an impostor. "You're really talking apples and oranges," she said.

While some physics students described Okazaki as "harmless," they said her presence could be worrisome.

"It is a little creepy that there's someone always there," Wells said. "Sometimes she likes to talk a lot, even when people are busy. At times I know it can get a little annoying."

At one point, Okazaki had to be scolded for bothering the physics theory group, Rajendran said.

"She used to spend a lot of time on our floor trying to talk to people," Rajendran said. "That was kind of a pain because it was distracting us from doing work. She stopped doing that after we sort of very harshly told her not to come there."

Okazaki also used to prop doors open in the building, apparently because she didn't have a card key, triggering concerns about security or theft, students said.

Hundreds of thousands of dollars in scientific equipment has been stolen from campus science buildings in recent months, university officials said, but all the students interviewed said they were confident Okazaki had no involvement.