Cryptojacking is when a cybercriminal uses someone else’s computing power to mine for cryptocurrencies without their consent. This is because mining for digital currencies like Bitcoin, while still lucrative, is more expensive than it used to be. Some attacks are designed to steal the currency outright, by robbing digital wallets, but the majority of threats come in the form of cryptojacking Many attacks take advantage of flaws in existing software, or even by using drive-by downloads embedded in online ads.
Source: https://www.mcafee.com/blogs/consumer/consumer-threat-reports/why-you-need-to-know-cryptojacking/