The Pirate Bay, the Internet's largest torrent portal, is back at running a cryptocurrency miner after it previously ran a short test in mid-September.

The technology in question is called Coinhive, a JavaScript library that allows The Pirate Bay's owners to make money by using the site's visitors computers to mine Monero, a very profitable cryptocurrency.

No way to opt out

The Pirate Bay tested Coinhive for a day, on a weekend, in September, calling it a test. Now, it appears that the Coinhive script is back again, and to everyone's surprise, there's no way to opt out.

The Pirate Bay operators said in September they wanted to test Coinhive as an alternative to running ads on the site. Currently, the cryptocurrency miner runs alongside the site's usual ads.

Because there was no official announcement from The Pirate Bay staff, some experts suggested that the Coinhive script might be loaded via rogue advertising.

Coinhive has a UI widget, but it's not deployed on The Pirate Bay

Coinhive works by running complex mathematical equations used to verify Monero transactions. These operations take a toll on the computer that runs them, which is easily observable by high CPU usage and a slowdown of the entire PC.

Coinhive, which is a legitimate business, promotes its business as an alternative to classic ads and recommends that site owners add warnings to let users know when the script is loaded.

Recently, the company also launched a simple UI widget that site operators can load and let users control when and how the script runs. This widget does not appear on The Pirate Bay site.

Most site operators don't do such things, and the script is a favorite among malware developers. Lately, another service named Crypto-Loot also popped up as an alternative to Coinhive and is currently gaining its own fanbase among malware devs.

Because of all the recent Coinhive abuses, most ad-blockers and antivirus engines will block the script, or at least notify users that the script is running. There are also Chrome extensions that can block local, in-browser cryptocurrency mining [1, 2, 3].

h/t Nic Carter