One thing to remember about the Internet: Nothing is free. That’s especially true of torrent sites like the Pirate Bay, Kickass Torrents, Popcorn Time or any of their imitators that offer free downloads of TV, movies and music.

A new study conducted by the nonprofit Digital Citizens Alliance, a cybercrime research group, and RiskIQ, a cybersecurity firm, found one-third of 800 torrent sites distributed malware to unsuspecting users between June and August 2015. That was enough to expose at least 12 million Web users to potential attacks every month, the researchers said.

Torrent sites need to make money to keep the lights on, but downloaders might not be comfortable with their business model. The sites make money by selling ad space to malicious advertisers, who then harvest user profiles and sell them on the dark Web for $20 to $45 per user. The ad revenue and sales of user information amounted to $70 million in revenue in 2015, the researchers said.

“Movies are digital bait,” said Tom Galvin, executive director of Digital Citizens Alliance. Pirate sites have always stolen from content creators by making shows available for free, but now they’re stealing from people who download those shows, as well. “Consumers are defenseless, and this is really exploiting and abusing them.”

Victimized computers are traditionally compromised via malicious advertisements that insert malware onto a user’s computer or point them to an infected site. But 45 percent of the malware from piracy sites comes in the form of a drive-by download, which corrupts a user’s computer without the user ever clicking a single link. That spyware then scans a user’s computer for personal details, including Social Security information, that can be sold on various online black markets.

“When you visit mainstreams sites, things are naturally happening without you clicking anything: pictures are being downloaded, ads are generating,” Galvin said. “What’s happening now is that users can click on one of these content sites and decide not to watch a movie, but the malware is already on their computer scraping for their Social Security number. That’s used to mimic and adopt your online persona, access banking information, and in some cases people are getting credit fraud notifications.”

Researchers used legitimate media sites like Crackle and Hulu as a control group. They compared the number of malware incidents on those sites to hundreds of piracy sites on the U.S. Trade Representative’s Notorious Markets Report and Google’s Transparency Report, which flags copyright scofflaws. The latter category reads like a who’s who of the most influential movie torrent websites of the past decade: the Pirate Bay, Kickass Torrents, ExtraTorrent, multiple Torrentz forks, Putlocker and others.

Two percent of the mainstream websites had a malware incident over the month data was collected, compared with 33 percent of the illegal movie houses.

“The sites that could be clean in the report could be infected tomorrow,” said Ross Reynolds, director of product management at RiskIQ. “They tend to have flexible infrastructure, so that if they’re taken down they always have something ready to shift to.”

Sophisticated Burglary Tactics

Drive-by downloads victimize users by quietly scraping their machine for any usable personal information, leading to financial fraud and any number of other possibilities. But the other 55 percent of malware installations were just as concerning – they just tricked users into inviting them inside instead of breaking in with a digital crowbar.

Photo: Digital Citizens Alliance, RiskIQ

The most prevalent category was Trojan malware, which, like the Greek wooden horse that inspired the name, lures victims into installing something that seems safe to their machine, only to find out later that that antivirus program, email attachment or other form of bait came equipped with spyware.

Remote access Trojans (RATs) are a particularly nasty subset of Trojan malware capable of taking control of a target computer to steal financial data, passwords or innocuously turn on a laptop’s camera. At least 10 RATs targeted torrent users during the research period and the most popular, Xtreme Rat, was recently used to infect computers used by the U.S. State Department and Israeli military personnel.

Adware was the next most popular form of malware distribution, making up 29 percent of the threat landscape. The problem (often involving malware-infused popups or banner ads) has been a unique challenge for the piracy community because so many sites support themselves by selling ad space to shady companies willing to deal with criminals for the right price. Even the Pirate Bay and Kickass Torrents, two of the biggest players, have failed to deal with the issue adequately in the past year.

Researchers did not trace the attacks back to their source, though they also found “quite a bit” of ransomware.

“To make a long story short, there was a lot of it,” Reynolds said of ransomware, the form of attack that holds a user’s computer hostage until they pay a fee, often in the thousands of dollars. The encryption used to lock users out of their data is so complex that an FBI special agent admitted in October the bureau often has no choice but to advise victims to pay up.

Stopping piracy has proved vexing for the content industries since Napster popularized peer-to-peer downloading almost 20 years ago. That’s mainly because, when a website is blocked, it’s often blocked by a single Internet service provider in a single country. Even when an international police force raided the Pirate Bay and confiscated the site’s servers, the piracy community simply moved to other sites, and illegal downloads barely dipped.

Obviously, the best way to avoid increased exposure to malware, particularly drive by downloads, is to avoid piracy sites entirely. But the Pirate Bay and Kickass Torrents are among the most popular websites in the world, proving that a generation of users just can’t resist the temptation to download free Oscar-nominated movies before they’re out of theaters.

“I’m not even slightly surprised by what you say about piracy sites and malware," said Brett Danaher, an assistant professor of economics at Wellesley College and the co-author of a major 2015 study on the effect of blocking piracy sites. "Given that they can profit by getting malware onto my computer, why wouldn’t they do this?”