Cryptojacking, which exploded in popularity this fall, has an ostensibly worthy goal: Use an untapped resource to create an alternative revenue stream for games or media sites, and reduce reliance on ads. It works by embedding a JavaScript component in a website that can leverage a visiting device's processing power to mine a cryptocurrency (usually Monero). Each visitor might only do a tiny bit of mining while they're there, every user lending some hash power over time can generate real money.

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