What is ASCII smuggling?

ASCII smuggling is a technique that uses a special range of Unicode tags to encode characters that are invisible to humans but readable by computers. It was originally used to hide malicious prompts in AI attacks.

How are spammers using ASCII smuggling?

Spammers use ASCII smuggling to hide keywords in spam emails, making them invisible to human readers but still processed by email filters, thereby evading detection.

What did Microsoft observe?

Microsoft observed a massive increase in spam using ASCII smuggling, with detections spiking from about 21,000 per day to over 1.3 million and then to 2.5 million within four days in early February.

AI Safety & AlignmentArs Technica AISep 4, 2026Sep 5, 2026, 06:03 JST

ASCII smuggling now used by spammers

Send on LINE

3 Key Points

What happened
ASCII smuggling, a technique once used to hide malicious prompts in AI attacks, is now being used by spammers to evade email filters. Microsoft observed a spike in detections from roughly 21,000 per day in early February to over 1.3 million, and then 2.5 million within four days.
Why it matters
The technique uses Unicode tags that are invisible to humans but readable by computers, allowing spam to bypass filters without raising user suspicion. Microsoft explained that the same property that made it useful for smuggling instructions into models is now used to obfuscate keywords before detection.
What to watch
The surge is likely a trial run, so the test is whether spammers can sustain evasion as filters adapt. Watch whether Microsoft’s detection counts stay near the 2.5 million peak within four days.

Not sure about something? Ask the AI

Questions and answers are published on this page.

Summaries like this, in your inbox every morning.

Get news like this every morning, free

Context & Analysis

The adoption of ASCII smuggling by spammers marks a shift in how a technique originally designed for AI-specific attacks is being repurposed. Microsoft's data shows a dramatic increase in detections, from roughly 21,000 per day to over 1.3 million, then 2.5 million within four days, indicating a rapid and widespread adoption. The technique's effectiveness lies in its use of Unicode tags that are invisible to humans but readable by computers, allowing spam to bypass filters without raising user suspicion. This evolution suggests that security measures must consider both AI-specific attacks and traditional spam campaigns, as the same underlying mechanism can serve different malicious purposes. The surge persisted for months before falling off in mid-May, suggesting that spammers may cycle through different evasion techniques as defenses adapt.

FAQ

What is ASCII smuggling?: ASCII smuggling is a technique that uses a special range of Unicode tags to encode characters that are invisible to humans but readable by computers. It was originally used to hide malicious prompts in AI attacks.
How are spammers using ASCII smuggling?: Spammers use ASCII smuggling to hide keywords in spam emails, making them invisible to human readers but still processed by email filters, thereby evading detection.
What did Microsoft observe?: Microsoft observed a massive increase in spam using ASCII smuggling, with detections spiking from about 21,000 per day to over 1.3 million and then to 2.5 million within four days in early February.

Ars Technica AIRead Original Article

Send on LINE

AI news that matters for your work, delivered every morning.

Pick your industry and the AI tools you use, and get news related to your work every day.

Get it free

Free · 30 seconds with Google · unsubscribe anytimeWhat is AIToday? →

Ask AI

Ask AI anything about this article. The AI reads this article, earlier AIToday articles, and Wikipedia, and cites its sources. Q&As are published on this page for other readers too.