Recently, publishers have begun encrypting their software packages to prevent the user from installing the software without accepting the license agreement or violating the Digital Millennium Copyright Act (DMCA) and foreign counterparts. [Citation required] A common criticism of end-user licensing contracts is that they are often far too long for users to spend time reading them carefully. In March 2012, the PayPal end-user license agreement was 36,275 words and in May 2011, the iTunes agreement was 56 pages long.  The sources of information that reported these results stated that the vast majority of users do not read the documents because of their length. The DMCA specifically provides for reverse software engineering for interoperability purposes, so there has been some controversy over whether contractual software licensing clauses restrict this situation. The 8th Davidson – Associates v. Jung found that such clauses are enforceable after the decision of the Federal Circuit of Baystate v. Bowers.  A free software license gives users of this software the right to use, modify and redistribute creative works and software that are both prohibited under copyright and are generally not licensed with proprietary software. These licenses usually contain a disclaimer, but this feature is not just for free software.  Copyleft licenses also contain a key add-on clause, which must be followed to copy or modify the software, requiring the user to provide source code to the factory and distribute its changes under the same license (or sometimes compatible); effectively to protect derivative works from the loss of original permissions used in proprietary programs. In addition to the doctrine of implied exhaustion, the distributor may include patent licenses with software. Most retail software licenses reject (as far as local laws permit) any guarantee on the performance of the software and limit liability in case of damage to the purchase price of the software.