ClamAV
Antivirus engine for detecting trojans, viruses and malware
...Originally designed for Unix environments and email security, it has evolved into a flexible antimalware toolkit capable of identifying millions of viruses, worms, trojans, and other threats. The software includes a command-line scanner, an automatically updating signature database, and a scalable multi-threaded daemon that enables high-performance scanning in production environments. ClamAV is widely used in mail gateways, file servers, and security pipelines because it can inspect compressed archives, common document formats, and executable files. Its bytecode signature system allows advanced detection logic while ensuring signatures are trusted and securely distributed.