A man wearing a mask has exposed himself to 13 women -- all but one Asian -- inside Penn State University main campus dormitories and in three off-campus apartments, State College police and a university spokeswoman said Wednesday.

The two latest incidents occurred last weekend in the borough of State College, while others were reported throughout the last year. University and borough police are coordinating their efforts, and patrols on the 44,000-student campus have been increased.

Investigators have not said definitively if they are looking for a single suspect, though in many of the incidents victims reported similar behavior from a suspect described as a college-aged white or Asian male.

The 10 on-campus incidents, which involve locations including the East Halls and North Halls complexes, date from Aug. 10, 2009, to Aug. 18 of this year. Initially, they involved laundry rooms, hallways and bathrooms, but more recently occurred in a residence room whose occupant left her door unlocked, according to university police.

The suspect wore a surgical or ski mask and in some instances was naked, Penn State spokeswoman Lisa Powers said. None of the victims was physically assaulted, though in some cases the suspect may have tapped on a victim's shoulder.

"There's always a concern about escalation," Ms. Powers said. "He's moved from being in hallways to opening unlocked doors."

Penn State students generally need a swipe card specific to their dorm to enter it, and Ms. Powers said there was no sign of forced entry. "He's getting in somehow, possibly through students who just don't know that this is the actor," said Tyrone Parham, deputy chief of university police.

Ms. Powers said nine of the 10 campus victims were Asian, as were the three borough victims, according to State College police.

All three off-campus reports involve first-floor apartments, including two incidents overnight Friday at the Nittany Gardens Apartments at 445 Waupelani Drive, borough Police Lt. Keith Robb said. In those cases -- like an earlier one in June at a nearby complex -- the suspect entered the apartment through a window, a sliding glass door or a balcony, police said.

Police urged students not to allow others to enter a dorm behind them who do not use their identification card and to keep doors and windows secure. They asked those who spot anything suspicious or have information to call Penn State police at 814-863-1111; borough police at 814-234-7150, or the Centre County Crime Stoppers at 877-99-CRIME. A reward is being offered.

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.