SpamBrain is Google’s AI-based spam-detection system, first publicly acknowledged by Google in 2021 and significantly expanded in subsequent years. Unlike rule-based spam filters that target specific known tactics, SpamBrain uses machine learning to identify spam patterns it has not seen before, making it more adaptive to evolving manipulation techniques. Google has stated that SpamBrain catches the vast majority of spam before it ever reaches users, operating continuously rather than as periodic updates. In March 2024 Google cited SpamBrain as central to its expanded spam policies targeting scaled content abuse, expired domain abuse, and site reputation abuse. The system evaluates both the content of pages and the link signals pointing to them, enabling it to neutralise the value of links generated by link schemes even without publicly disclosing the exact detection logic.