Jennifer Park ’05 had recently been to a birthday party, so she was not surprised when she received an e-mail from the host with the subject line “new photos from my party!”

But when Park opened the attachment, a window unexpectedly popped up, and she realized she had a virus.

After midnight on Monday, a computer “worm” began to spread over campus via e-mail, infecting Windows machines. Bearing an attachment labeled “,” the virus proliferates by mass-mailing itself to recent contacts and members of each infected person’s address book.

Philip Long, the director of Information Technology Services, said he believes a lot of undergraduates have received a copy of the virus, which he noted is only replicated and passed on by Microsoft Outlook Express users.

“It’s reasonably widespread according to anecdotes,” Long said.

He added that there is no definite way to know the number of affected students.

Long said the virus was first reported at 12:30 a.m. on Monday.

“It probably entered the Internet the evening of Saturday. Virus updates were already available as of [Monday] morning,” Long said.

The Yale ITS Information Security Office sent an e-mail to the Yale community around 10 a.m. on Monday morning, advising Yalies not to open the attachment or click the link contained in the virus e-mail. The message from ITS arrived after many students had already encountered the virus.

Leveille McClain ’04 said he first learned about the computer worm from his roommate, who opened the attachment. Despite the fact that his roommate alerted him to the virus, McClain said he still does not think he would have opened the attachment.

“I knew two of the people who had sent it to me, but neither of them had had parties so I just deleted them,” McClain said.

The virus quickly circulated throughout the Yale campus, reaching some people multiple times. Peter Chen ’04 said he received approximately 25 copies of the virus.

“When I checked my mail [Monday] morning, I had a couple of the virus e-mails from different people. One of the people I knew, so I opened it,” Chen said.

He added that he clicked on the attachment out of curiosity.

Pierson College computing assistant Andrew Hudson ’03 said infected users can update their versions of Norton Anti-Virus to get rid of the virus.

“Open up Norton, press the Live Update button,” Hudson said. “It will download the newest virus definitions.”

Long said the ITS Web site makes recommendations about how students can protect their computers.

“Whenever you get an attachment, even if it’s from someone you know, consider if you want to open it,” Long said. “Watch out for funny name attachments. We’re always trying to improve our own defenses. [But] it’s inevitable that some of these things will get through.”