Unnoticed for years, malware turned Linux and FreeBSD servers into spamming machines

From Help Net Security:

Unnoticed for years, malware turned Linux and FreeBSD servers into spamming machines

For over 5 years, and perhaps even longer, servers around the world running Linux and FreeBSD operating systems have been targeted by an individual or group that compromised them via a backdoor Trojan, then made them send out spam, ESET researchers have found.