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ASCII smuggling crosses over from AI prompt injection to phishing evasion
Microsoft details high-volume phishing campaign using ASCII smuggling (Unicode tag chars) for filter evasion, peaking at 2.3M messages.
Microsoft researchers observed a high-volume finance-themed phishing campaign using invisible Unicode tag characters (U+E0000–U+E007F), a technique known from AI prompt injection research as ASCII smuggling, to split lure words like 'funding' and evade email filters. Telemetry from Microsoft Defender for Office 365 showed signature hits jump from roughly 21,000 messages on February 8, 2026 to more than 1.3 million on February 9, peaking above 2.3 million on February 11, with elevated weekday activity lasting approximately three months. The discovery emerged from prompt injection protection research, showing AI-era evasion techniques crossing into traditional phishing. Most messages were flagged by layered Defender protections rather than a single Unicode-specific signal.
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Hackers Favor US Eastern Business Hours in M365 Phishing Campaign
KnowBe4 tracked 29,785 phishing emails abusing Microsoft 365 Direct Send to spoof internal senders while timing sends to US Eastern business hours.
KnowBe4 Threat Lab observed 29,785 confirmed phishing emails between July and August 2026 abusing Microsoft 365's Direct Send feature, which lets devices and legacy apps send mail without a dedicated account. The emails appeared to come from trusted internal addresses such as HR or accounting, bypassing email gateways by connecting directly to Exchange Online MX endpoints, with activity peaking on Monday-Tuesday during US Eastern business hours and near-zero weekend volume. About 35% of the messages carried malicious attachments like fake invoices, voicemail alerts, and OneDrive shares, and 4,023 used reply-to addresses on different domains to capture employee responses. Researchers recommended strict DMARC enforcement, connector restrictions, DKIM signing, and checking for the 'X-MS-Exchange-Organization-AuthAs: Anonymous' Exchange header.
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