The Linux Virus Writing HOWTO describes how to write parasitic file viruses which infect ELF executables on Linux/i386. Contains a lot of source code. Every mentioned infection method is accompanied with a practical guide to detection.
You can download it from the following link: https://packetstormsecurity.com/files/download/26586/virus-writing-HOWTO-2002-08-15.tar.gz
Source: https://packetstormsecurity.com/files/26586/virus-writing-HOWTO-2002-08-15.tar.gz.html