Spammers Use 'ASCII Smuggling' to Evade AI Email Security Filters

Spammers are increasingly using ASCII smuggling, a technique involving invisible Unicode tags, to hide malicious keywords from AI-powered email security filters and bypass detection systems.

Microsoft Defender for Office reported a surge in these signatures, which spiked from 21,000 per day in early February to 2.5 million within four days before declining in mid-May.

By embedding invisible characters like U+E0020 into words, attackers disrupt tokenization in machine learning models, causing filters to misread terms like 'funding' while remaining invisible to human recipients.