Sony has released a software patch that removes controversial cloaking technology found earlier this week in its copy protection software.

Critics had slammed the software for being invasive and extremely difficult to remove because it uses some of the same "rootkit" cloaking techniques normally found in spyware or viruses.

Rootkit software uses a variety of techniques to gain access to a system and then cover up any traces of its existence so that it cannot be detected by system tools or anti-virus software.

The patch, posted to Sony's website, was to "alleviate any concerns that users may have about the program posing potential security vulnerabilities," Sony said in a statement. By installing the patch, users will not remove the copy protection software, called XPC, but they will make it visible to system tools and anti-virus software.

XCP has been shipping on some Sony music CDs since early 2005. Licensed by Sony from a Banbury company called First 4 Internet, XCP prevents users from making more than three backup copies of any XCP-protected CD. Sony will not say how many of its CDs use the software.

Critics had complained that because the software was virtually impossible to detect, hackers might somehow take advantage of it in order to hide their own malicious code from anti-virus software. They had also slammed Sony for not adequately informing users of how it worked and for making it extremely difficult to remove XCP. First 4 has described such concerns as "unnecessary."

First 4 and Sony went too far though, according to Mark Russinovich, the computer expert who first revealed how XCP works. "Not only had Sony put software on my system that uses techniques commonly used by malware to mask its presence, the software is poorly written," he wrote on his blog. "Worse, most users that stumble across the cloaked files... will cripple their computer if they attempt the obvious step of deleting the cloaked files."