An MIT expert is warning that Hub government agencies, businesses and personal PC users could be “paralyzed” if they fall prey to the same scheme that hit the Swansea Police Department — the latest victim of an Internet virus that forces computer users to pony up an online ransom for an encryption key to unlock their files.

“Once the files are gone, it’s like someone takes a sledgehammer to your computer,” said Massachusetts Institute of Technology professor Ronald L. Rivest, who co-invented the technology hackers are exploiting. “It could certainly happen again to government agencies or individuals. People need to be wary and keep good backups on separate servers or on separate hard drives.”

FBI spokesman Greg Comcowich said the agency is investigating after CryptoLocker ransomware — as the virus is known — took computers hostage at the Swansea Police Department Nov. 6.

“It gave us 100 hours to pay and it was literally a timer,” said police Lt. Gregory Ryan. “A big red screen comes up with a timer that says you have 100 hours to pay or your files will be encrypted forever.”

Ryan said the department finally decided to pay the $750 ransom demand for two bitcoins — a peer-to-peer online currency system that is difficult to track — several days after calling in computer experts and the FBI. He said the department’s files were recovered last Sunday after paying the hackers, and no information was compromised.

CryptoLocker ransomware infected more than 12,000 computers in one week — between Oct. 27 and Nov. 1 — and the hackers who created the virus are targeting U.S. computers, according to research released by anti-virus company Bitdefender Labs.

The FBI reports that the virus, which is transmitted through email links and attachments, encrypts the files of an infected computer with an RSA key. The key — which Rivest invented at MIT in 1977 with fellow researchers Adi Shamir and Leonard Adleman — is a complicated math algorithm based on two large prime numbers and impossible to crack.

“It’s sad to see our scheme being used for evil purposes,” said Rivest, who told the Herald the encryption is also used to protect online shopping transactions. “Trying to break these things with different computers just isn’t possible. That’s not going to be possible with the technology we have on this planet right now. You’re paralyzed unless they actually give you the key.”

Tan Nguyen of Alfa Computer in Woburn said he’s seen seven CryptoLocker cases in the past two months. He said he was able to help two of the virus victims recover the latest saved versions of their lost files, but the original files remained locked.

“Removing the virus is fairly easy, but the files are still encrypted once the virus is gone,” Nguyen said. “Unencrypting the data is really an impossible task.”