The link above will take you to an informational page at British Anti-Virus firm Sophos. Read it and use the link to download a tool which disables the Sony DRM, removes at least most of it and prevents it reinstalling.
Sophos is to be congratulated for such swift action on this. I'm sure others will follow.
Windows users are now taken care of on this issue. Word is coming around that Macs are also affected by the Sony rootkit. Details are still sketchy as I've been unable to find enough information in English and machine translations are inadequate. I'll keep looking.