The holiday season is a time for shopping for gifts, spending time with family and for some, hacking into the San Francisco subway system.

In fact, many, many computer systems in San Francisco were hacked this past weekend. So many, in fact, that the entire subway system has been left free to use until the computer problem is resolved.

The answer will come in the form of Bitcoin, as this is what the culprits have demanded in return for putting the computer system back online.

Over 2000 local computer systems affected

A strain of a computer malware, known as HDDCryptor, hit 2,112 computers within the San Francisco Municipal Transportation Agency, according to correspondence with the ransomware's masters. This has affected the railway system starting on Friday evening, continuing throughout Saturday, and as of Sunday night, there has been no news of a resolution.

CBS affiliate KPIX in San Francisco, says sources inside of the city’s transit agency told them on Saturday that the system was hacked days ago. Payment kiosks are out of service and cards can not be purchased.

"There’s no impact to the transit service, but we have opened the fare gates as a precaution to minimize customer impact," the transit agency's spokesman Paul Rose said.

"Because this is an ongoing investigation it would not be appropriate to provide additional details at this point.”

The perpetrators have made it very clear that this was not an accident, and the goal was to get Bitcoins. The infected computers displayed the following message:

"You Hacked, ALL Data Encrypted, Contact For Key ( ID:601.”

The hackers are seeking an even 100 Bitcoins to unlock these public service systems, which currently equates to around $73,000.

Hackers infiltrating private networks for Bitcoins is not a new or recent occurrence. Banks, police stations, hospitals and private sector businesses have been held up over the past two years in search of Bitcoin ransom, instead of cash. Obviously, Bitcoin itself is not the problem, but the computer experts would rather receive the digital currency than another more traceable form of payment.

Bitcoin works on a public Blockchain, so the payment, if made, could be tracked to a wallet. However, a mixing or laundering device for Bitcoin could be used to throw authorities off the trail.

Another problem with ransomware is the victim is trusting the criminal masterminds to release the computer systems after payment, which is not always the case. Many are held up for even more payments after the first one is made.