These rootkits have been available in the Unix world for years. Being used to repeatedly test systems permanently connected to the Internet years before the advent of Windows servers. Nothing new here. Just a scare thought up by the AV companies to sell more product.
'A "root kit" is a series of modified programs all centered around the idea of helping you to keep access to a Unix system once you have gained root priveleges there. It might path 'ls' not to show your files and directories. It might patch 'ps' now to show your processes. It might patch 'login' to always allow you in if you enter a special "magic" password. The possibilities are nearly unlimited.' Date: Apr 28 1996
"the root kit comes to mind .." Date: May 22 1995