Universal login trojan – Login trojan for pretty much any O/S. Tested on Linux, BSDI 2.0, FreeBSD, IRIX 6.x, 5.x, Sunos 5.5,5.6,5.7, and OSF1/DGUX4.0. Works by checking the DISPLAY environment variable before passing the session to the real login binary.
You can download it from the following link: https://packetstormsecurity.com/files/download/10614/ulogin.c
Source: https://packetstormsecurity.com/files/10614/ulogin.c.html