Facebook’s “Facebook Immune System” scans every single click on the social network for spammy messages. Only 4% of the entire network’s messages are spammy, and only 1% of users get hit with spam. Facebook says it has 750,000,000 users, but it has 25 billion of these clicks every single day. FIS will also raise an eyebrow at users who receive massive number of friending spree robot friends being friended out, likely a friending robot.”]
Source: https://gizmodo.com/facebooks-massive-security-system-scans-your-messages-t-5853567