Soon after the PSP was released, hackers began to discover exploits in the PSP that could be used to run unsigned code on the device. Sony released version 1.51 of the PSP firmware in May 2005 to plug the holes that hackers were using to gain access to the device. On 15 June 2005 the hackers distributed the cracked code of the PSP on the internet. Hackers refused to apply updates which would render their hacks unusable so Sony attempted to convince users that there was a benefit to upgrading by including new features in the firmware updates, such as a web browser, and not just security patches to plug the vulnerabilities. BusinessWeek dubbed this the "carrot-and-stick" approach.