Microsoft reports spike in Unicode-tag spam obfuscation

Microsoft reported a sharp rise this year in spam using invisible Unicode tag characters to obscure keywords from email filters. Its Defender for Office signatures rose from about 21,000 a day to more than 1.3 million on one day in early February, then reached 2.5 million within four days. The activity persisted for months before falling sharply in mid-May. The technique, known as ASCII smuggling, had previously drawn attention for hiding prompt-injection instructions from people while leaving them readable to language models.