If you've used The Pirate Bay to download TV shows and films, your computer may have been taken over and used to mine a virtual currency without your knowledge.
The Pirate Bay included code on some of its web pages that used visitors' machines to mine a virtual currency over the weekend without users consent.
The code generated coins for the Monero digital currency, which the site claims is an additional revenue stream, The Daily Mail reported.
The Pirate Bay's administrators have confirmed that the site has been using the code, but stress that it had only been an experiment to find alternatives to ad revenue.
Many users objected to the code being forced upon them without any warning.
A note on The Pirate Bay pages said: "Do you want ads or do you want to give away a few of your CPU [central processing unit] cycles every time you visit the site?"
Several people took to Twitter to express their annoyance, including Jeremy Williams, who tweeted: "I read that for 24 hours, The Pirate Bay is running bit coin mining through their browser, no warning. Use ad block and no script. Stay safe."
The miner can be blocked using a normal ad-blocker that can be downloaded online.
It is unclear if The Pirate Bay plans to use the code again.