Mark's Sysinternals Blog: Rootkits in Commercial Software

"By now many of you have heard that Symantec released a security advisory last Tuesday that reported its use of rootkit-like cloaking technology in its SystemWorks product. The Symantec use of rootkit-like cloaking raises the question of what exactly defines a “rootkit” and whether or not there is ever a justifiable reason to use cloaking. I’ll first describe Symantec’s cloaking and then I’ll move on to trying to answer these two questions."