Until recently, the policy of the Chrome Web Store has been to allow cryptocurrency mining extensions under the condition that this was its sole purpose. The intention was that if they were only mining-specific and that users were properly informed, they would know what they were getting into. But we can't always count on developers to actually follow the rules.
"Approximately 90% of all extensions with mining scripts that developers have attempted to upload to Chrome Web Store have failed to comply with these policies, and have been either rejected or removed from the store," wrote James Wagner, Extensions Platform Product Manager for Google.
Given the rampant spread of extensions that don't adhere to Google's policies, the company is cracking down on everyone. This means that the Chrome Web Store will no longer allow new extensions that specifically mine for cryptocurrencies. In addition, extensions that are already in the store that mine for cryptocurrencies will be kicked out prior to July 2018.
Wagner goes on to extol the benefits of its extension ecosystem for Chrome, and that he laments the fact that unscrupulous characters have ruined things for everyone. "This policy is another step forward in ensuring that Chrome users can enjoy the benefits of extensions without exposing themselves to hidden risks."
Back in late December, it was discovered that popular Chrome extension Archive Poster had been hijacked by Digimine malware, which was being used to mine Monero. Browser competitor Opera Software took a more aggressive stance against cryptojacking software by incorporating built-in anti-mining protection into Opera, Opera Mini and Opera for Android.