Cybercriminals Use Invisible Characters to Bypass Email Security Filters

Cybercriminals use invisible Unicode in emails to bypass security, targeting users with fake password expiration alerts.

By Content Team

Oct 29, 2025

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Security researchers have uncovered a new phishing technique where cybercriminals embed invisible Unicode characters in email subject lines to evade automated security systems. The attackers use MIME encoding with soft hyphens to fragment trigger words like "password" while keeping them readable to humans.

When viewed in email clients, subjects appear garbled in message lists but render normally when opened. The technique breaks up keywords that would typically alert security filters, allowing fake "password expiration" emails to reach inboxes.

The Internet Storm Center discovered this method targeting credential theft through fake webmail login pages. The invisible characters effectively turn "password" into "p-a-s-s-w-o-r-d" at the code level, fooling detection systems while appearing normal to victims.

Source: Cybersecurity News

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