Microsoft Detects 2.5 Million ASCII-Smuggling Spam Signatures in 4 Days
Updated
Updated · Ars Technica · Sep 4
Microsoft Detects 2.5 Million ASCII-Smuggling Spam Signatures in 4 Days
3 articles · Updated · Ars Technica · Sep 4
Summary
Microsoft Defender for Office saw ASCII-smuggling detections jump from about 21,000 a day to 1.3 million in early February, then hit 2.5 million within four days.
The technique hides spam keywords in 128 Unicode tag characters that computers can read but humans can barely see, letting messages slip past filters built to catch mass campaigns.
Microsoft said the same mechanism drew notice two years ago for concealing prompt-injection attacks on AI agents, but spammers have now repurposed it for email evasion.
The surge lasted for months before dropping sharply in mid-May, underscoring how AI-era obfuscation methods are spilling into broader cybercrime tactics.