Can Linux be infected by MalWare and is it a big concern? The answer to that question is both Yes and No: Yes, Linux can be Infected and No, it isn’t a big nightmare – yet.
Unless you downloaded the Unreal IRCd (Unreal IRC daemon) and installed it between November 2009 and June 2010 on your Linux server. There was a Trojan downloader in it. A Linux Trojan. See the Softpedia Article