Unicode Consortium Releases UTS #39 to Block Lookalike Attacks
UTS #39: Unicode Security Mechanisms
Unicode Technical Standard #39, version 18.0.0, defines security mechanisms for detecting spoofing in identifiers such as URLs, domain names, and email addresses. It specifies a General Security Profile that restricts uncommon and obsolete characters, plus IDN and email profiles, and provides confusable detection for whole-script and mixed-script lookalikes. Implementations can claim conformance either by following the spec unchanged or by documenting precise character additions and removals.
Because Unicode contains such a large number of characters and incorporates the varied writing systems of the world, incorrect usage can expose programs or systems to possible security attacks.