Block Cryptocoin Miners like coinhive.
Through the rise of Cryptocurrencies like BitCoin, LiteCoin, Ethereum, Ripple, Monero and many more, companies developed strategies to use third party hardware to mine Cryptocoins.
One popular approach is to use your hardware to mine coins like Monero.
If you wonder why your computer got pretty slow, it's possible that some websites mine coins right in your Browser. CoinBlock prevents this by blocking mining requests before they can start working. CoinBlock also ships with a mechanism that lets you whitelist certain websites.