Google announced it is pulling cryptocurrency mining extensions from its Chrome Web Store April 2 after “90%” failed to comply with its rules.

In a blog post, extensions platform product manager James Wagner said that the move was in response to analysis of malicious “cryptojacking” present in extensions.

The term refers to when users downloading an extension of any sort unwittingly start mining cryptocurrency without their consent.

“Over the past few months, there has been a rise in malicious extensions that appear to provide useful functionality on the surface, while embedding hidden cryptocurrency mining scripts that run in the background,” Wagner claims.

While formerly allowing cryptocurrency mining extensions that mined as their sole purpose, Google will now ban new candidates from entering the Web Store and remove existing ones by June.

Only one in ten extensions involved in mining adhere to Chromium’s policies on disclosure, according to Wagner.

“Unfortunately, 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,” he adds.

June also marks the start of Google’s other, more controversial cryptocurrency-related ban, that referring to cryptocurrency advertisements, which will disappear from Google Adwords.