"It is impossible, in an urban environment such as ours, to make ourselves invulnerable, but we can become better informed about the risks with which we must live," wrote Eugene C. McAfee, Lowell House's Allston Burr Senior Tutor.

"Since the geography [of the robberies] is so spread out, it's impossible to say 'avoid this one area,' " McNamara said.

Instead McNamara and HUPD's newly appointed crime prevention specialist Steven G. Catalano have drawn up a community advisory and safety precautions for students.

"As always, please be aware of your surroundings, and familiarize yourself, with the location of the nearest emergency call boxes (blue light phones)," the advisory reads.

"When possible, walk in groups along well-lit, heavily traveled areas," McNamara added.

McAfee also asked students to carry safety whistles. Students should never display valuables such as cell phones in public, he added.

Leverett House Master Howard Georgi sent an e-mail message to students in the hours after the assault warning them of the incidents, and said he plans to follow up with some House meetings to discuss safety.

"It doesn't hurt to be vigilant," said Georgi.