The nation's top Internet service providers sent more than 1.3 million infringement notices to alleged copyright scofflaws last year, according to a study released Wednesday.

The system works by matching IP addresses to account holders, and the notices were sent by just five ISPs participating in the so-called "copyright alert system" (CAS) that commenced in February 2013, a US program strongly backed by the Obama administration and run by the newly created Center for Copyright Information. Those ISPs are AT&T, Cablevision Systems, Comcast, Time Warner Cable, and Verizon.

Subscribers can get two notices for "educational" purposes that their accounts have been used to commit infringement. Upon a third and fourth notice, the subscriber must respond and acknowledge it. On the fifth and sixth notices, consumers may have their speeds throttled.

The program is expected to expand dramatically, too. According to the report by the Center for Copyright Infringement, "the program is slated to at least double the number of notices sent and processed in size in the coming year." The report (PDF) said there were 722,820 one-time "alerts" or notices to customers, 214,654 second alerts, 165,065 third-time alerts, 94,599 four-time alerts, 60,477 five-time alerts, and 37,456 six-time alerts.

Backers of the program say it's not designed to terminate account holders, even if they get more than six strikes. But the Digital Millennium Copyright Act requires ISPs to terminate services for repeat offenders.

Cary Sherman, the chairman of the Recording Industry Association of America and one of the top backers of the program, was cautiously optimistic about the results. "Does that all mean we can make a declaratory judgment that we’ve won the piracy fight? Of course not. This program was never intended to do that. But that CCI was finding fewer instances of piracy within the parameters of this program means that people were getting the message and going elsewhere for their music," Sherman said on the RIAA's blog.

Content owners were not provided access to the identities of the account holders who allegedly downloaded or shared infringing material on sites like The Pirate Bay and KickassTorrents.

Here's how the program works, according to the report:

The process begins with the content owners identifying a list of content files (films, music tracks and albums or television programs) for their technology vendor to focus on for a particular period of time. That list is then sent to their technology vendor and is updated continually. Currently, all of the member content owners use the same vendor to generate notices, a company called MarkMonitor. This vendor is responsible for scanning public P2P networks to identify instances where the files containing the listed content assets are being shared without authorization. For every single notice, the company employs a sophisticated process to verify that the file shared does indeed contain copyrighted content and that the IP addresses identified can be matched to one of the CAS' participating ISPs.

The study said there were 47 successful challenges to notices out of a total of 265 challenges. "The vast majority of those were based on an 'unauthorized use of account' defense, indicating that the account holder had made a satisfactory case that someone other than the account holder or a known (authorized) person was using the account in question to engage in impermissible P2P file sharing of copyrighted content," the report said.

The program does not prevent rights holders from filing suits against their targets. The US Copyright Act allows damages of up to $150,000 per infringement.