What are Browser Crypto-miners?
Ok, this is a bit complicated! To understand what browser based crypto-currency miners are you first need to understand (roughly) what crypto-currencies are.
Don't worry, we'll keep it as simple as we can...
What is Crypto Currency?
Crypto currency is an attempt to create new forms of currencies/money as alternatives to more traditional currencies or things which hold value and can be traded (eg. Gold, Dollars etc).
There are many types of Crypto-currencies; Bitcoin is the most well known one, but others also exist. Some organisations (called "Exchanges") will trade different crypto "coins" for traditional money (eg. They'll trade Bitcoin for American Dollars).
The subject of Crypto Currencies is very complex, confusing and there are very different opinions as to whether "crypto-currencies" are "good" or "bad"; we are attempting to keep this as simple and neutral as possible for the non-techies to understand what crypto-miners are.
The "crypto" in the term "crypto-currency" doesn't actually refer to "cryptography" (the act of encrypting information to keep it unreadable by other people), it refers to the fact that difficult mathematical operations (based on a subset of cryptography mathematics called "hashing") are used by software to generate "crypto-coins" and to trade them between people/organisations.
In other words, to generate (or "mine") new "coins", it takes a lot of time and computing power.
"Mining" new "coins"
As we all know, computers cost money to buy and to run. They use more electricity (and thus cost you more) when they are being used to perform difficult calculations (instead of sitting mostly idle).
Traditionally, to mine new crypto coins, a person (or group of people) would buy expensive computers and spend a lot of time and money running them to perform the difficult calculations to generate crypto coins.
In other words, when you visit a website with an embedded crypto-miner in it, your computer and electricity is used to try to generate crypto-coins for the owners of that website.
Legitimate Browser Crypto Mining?
Some website owners have argued that getting their visitors to mine crypto-currency for them while they use their website is a fair trade... After all, websites cost money to create and host, so why not get paid by your visitors?
Whether you agree with this is a personal decision, and from one perspective, we can actually kind of understand their point of view. The problem seems to be that most visitors aren't aware that this is happening and that their computers, electricity and money are being used without their direct permission to mine cryptocurrency for the website they're visiting.
Fortunately this doesn't seem to be a practice that's too widespread at the moment, but things may change in the future. If websites do use their visitor's computing power to mine crypto currencies then at the very least they need to be extremely up-front about the fact that they're doing it.
Blocking Crypto Miners
The practice of website owners doing this to unsuspecting visitors is widely frowned on. Bear in mind that it's also possible that a website might be broken into by criminals and secretly have crypto-mining software installed on it, unbeknownst to the owners of the site.
Blocking Crypto-miners in Firefox
In May 2019 Firefox started to block crypto mining malware by default.
Firefox groups the setting for blocking crypto-miners with their cookies setting. Please read our guide on changing cookie settings with firefox for more information.
Blocking Crypto-miners in Chrome
Chrome doesn't have this functionality built into it (yet?), so to block Crypto miners in Chrome you'll need to rely on a browser extension.
We have no affiliation with it, but minerBlock seems to be reputable and effective in achieving this.
Blocking crypto-miners in Opera
Opera was the first web browser to block crypto-currency miners. Opera Version 50 included this functionality in January 2018. You can change this setting in their AdBlocker preferences. Read their Press release.
Blocking crypto-miners in Safari
There doesn't seem to be any extensions for Safari which are directly aimed at preventing cryto-miners, however it does seem that two Ad Blocking extensions may provide this functionality. Check out AdGuard and 1Blocker and see if they work for you.
Blocking crypto-miners in other web browsers
If your web browser has an Extension or Add-on Store, try searching for crypto currency miner blockers.
There may be other anti-malware solutions which exist, however we can't recommend any particular one.
Another option would be to switch your browser to one which supports blocking crypto-currency miners.
Test if you are vulnerable to Browser Crypto Currency miners
The makers of the Opera browser have built a wonderful tool to test if your web browser is vulnerable to browser based crypto miners (which is sometimes known as Crypto-jacking). Check out: cryptojackingtest.com and click the "Start" button.