Several media outlets, including this CNET article, are reporting that Sony-BMG is responding to complaints about how their DRM adds hidden files by offering a patch for their CD-based DRM that was the subject of vociferous complaints and negative comments. The patch is being issued to antivirus companies so that the software can't hide. Sony-BMG and their copy protection partner First 4 Internet are taking this approach because many observed that the techniques being used by First 4 Internet could encourage virus writers to do the same. Snippets from the CNET article:
The anticopying technology included a tool called a "rootkit," often used by virus writers. A rootkit takes partial control of a computer's operating system at a very deep level in order to hide the presence of files or ongoing processes.
Rootkits, while not intrinsically malicious, are viewed with deep suspicion by many in the software development community. They are extraordinarily difficult to find and remove without specific instructions, and attempts to modify the way they act can even damage the normal functioning of a computer.
In the case of the First 4 Internet software, attempts to remove it manually rendered the CD drive of the computer inoperable, Russinovich [who called attention to the problem] found.