The decision to replace MediaSentry, if true, may have been influenced by the increasing amount of attention paid to its methods. MediaSentry has been operating in a legal gray area for quite some time and has come under fire before, accused of investigating without the proper licenses, performing illegal searches, covering up evidence and other “questionable” tactics. The RIAA may be seeking to distance themselves from the company.
Then again, considering the RIAA's history, nothing MediaSentry has done seems all that bad in comparison. Neither the RIAA nor MediaSentry have officially commented on such a decision yet.