Have you heard of cryptojacking? It's the practice of secretly using your computer's resources to mine cryptocurrency without the user's permission.

Typically, you'll see the practice on shady websites — popular Bittorrent site The Pirate Bay appears to have experimented with it at one point — but a cryptojacking program has recently been found in a popular Chrome extension.

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BleepingComputer reports that Archive Poster, a Chrome extension that helps Tumblr users reblog and repost from other blogs, also runs Coinhive, a cryptojacking program that secretly mines the cryptocurrency Monero using your CPU.

This is noted in several user reviews in the Chrome web store.

"Do not use this extension as it comes loaded with a cryptocurrency mining script. Once installed it makes requests to coinhive which eats up your CPU time and slows your computer down massively. Avoid," one user wrote.

Archive Poster appears to be quite popular with a total of 105,062 users. Unfortunately, despite recent negative reviews the extension still has a very good overall grade.

While cryptojacking software is not as dangerous as common malware — it typically doesn't do damage to your computer or files — it's annoying as it uses your CPU time and potentially slows down your computer considerably.

On the other hand, while mining cryptocurrency on your home computer isn't very lucrative lately, having tens of thousands of computers mining can be very profitable for the extension's developer (or the hacker who had managed to infect the extension with the cryptojacking software).

Security researcher Troy Mursch has been tracking the cryptojacking phenomenon and has reported on numerous instances of this practice, most recently on telecom Movistar's official website.

#Coinhive malware found on official @movistar_es website in latest high-profile case of #cryptojacking.



Movistar is a major telecommunications brand owned by @Telefonica, operating in Spain.https://t.co/EnQH2bm4go pic.twitter.com/HorQOl8rD4 — Bad Packets Report (@bad_packets) December 29, 2017

Coinhive, the cryptojacking software that's used in the Archive Poster extension, is freely available to download and is advertised as a way to "monetize your business with your users' cpu power". However, websites and software that use it without a clear warning to users are usually frowned upon at the very least.