STATEN ISLAND, N.Y. -- An overnight intruder smashed several windows and gained entry into Rep. Michael Grimm's New Dorp headquarters over the weekend, possibly tampering with computers inside the office, authorities said.

Grimm's staff discovered the damage Sunday morning -- two large chunks of cement and some smaller rocks had been hurled through three, 4x8-foot vertical windows, according to a campaign spokeswoman. They also believed that someone had deleted computer hard drives. The congressman and his campaign staff believe the vandalism was staged to cover up the computer tampering.

On further inspection it was determined the intruder had caused a different type of damage -- someone installed the Linux operating system on the office's computers, Grimm told the Advance Sunday night, and in the process wiped the hard drives clean. "All of my polling data, all of the data from my IDs of voters, and a bunch of other campaign information. But fortunately we had everything backed up from literally hours before, so we don't lose anything because we have backups," Grimm said.

He has no doubt his office was targeted, and called the incident cowardly.

"Whoever did this, the people responsible are very ignorant, and they don't understand that this is not just an attack against me or my campaign. This is an attack against a federal campaign office, which is an attack on our democracy as a whole. It's an attack against what we stand for, for free elections," he said.

"You can disagree with my policies. That's what debates are for. That's why you have the opportunity to vote for a different person to represent you. This ignorance, of violence, I would expect in the Middle East. You know, that wouldn't shock me at all. But here on Staten Island, a family-based community, we're better than that."

Nathan Smith, spokesman for the lawmaker's Democratic challenger, Mark Murphy, issued the following statement Sunday: "There is never any place for violence or vandalism in an electoral campaign or political debate. We hope that the police quickly apprehend whomever was responsible for this criminal act and prosecute all parties involved to the fullest extent of the law."

Grimm, a first-term GOP congressman and former FBI agent whose district also includes a portion of Brooklyn, is locked in a battle for re-election against Murphy.

The campaign headquarters is located on Hylan Boulevard near the New Dorp branch of the U.S. Postal Service.

The intruders didn't get access to personal information of the campaign's volunteers, which is in a separate location, Grimm said.

After his staff discovered the break-in at 9:30 a.m., Grimm said he got a call at about 10:45 a.m., while he was on his way to Mass at Blessed Sacrament R.C. Church in West Brighton with Rep. Peter King (R-Long Island).

Grimm speculated that the break-in is part of an ongoing effort against him.

In recent weeks, several "Grimm for Congress" lawn signs have vanished from supporters' yards, and a small billboard was stolen. His campaign plans to publicly release a video of a middle-aged woman they say is seen walking a dog and stealing signs.

Earlier in the week, the computers shut down and rebooted themselves in the middle of the night, Grimm said, and though the campaign first believed that was accidental, now they're suspicious, he said.

"I'm thinking that someone must have had a key. It was the old Villa Marin," Grimm said, referring to the former car dealership that is now his headquarters. "The locks have not been changed since it was Villa Marin, so hundreds of people could have keys to that space. We have no idea who. Someone could have made a key. There's a million ways someone could have got a key."

The campaign had no alarm system, he said.

"Other than the computers themselves, and some phones, there's not really anything of value. There's nothing really of value in the campaign office except the data," Grimm said. "We never expected something like this. Here on Staten Island, most people don't worry about this type of thing. It's a safe borough."

Grimm was on the scene Sunday afternoon with representatives of the NYPD, and his campaign has also notified Capitol Police of the crime.

"In fact, one officer said to me today they see this as a crime against the government, because I am a sitting United States congressman and they take it very seriously. You know, especially in light of what happened with Gabby Giffords, we're not in the world today where we can shrug things off," Grimm said, referring to the Jan. 8, 2001 shooting of Rep. Gabrielle Giffords, an Arizona Democrat, outside a Tucson supermarket. "Violence is violence. Throwing large stones and concrete through the window is an act of violence, and we've got to take it seriously."

A spokesman for NYPD Deputy Commissioner of Public Information Paul Browne said Sunday night that the incident is being investigated as an act of criminal mischief, adding, "NYPD Computer Crime will investigate further any assertions that computers were tampered with."

It's not the first time Grimm has been the apparent victim of a theft -- in February, a mailbox engraved with an American eagle was stolen from outside his New Springville duplex.