Sony had put significant effort into blocking custom firmware and other third party devices/content from the PSP, but their effort was in vain. In July 2007 Dark_AleX officially stopped his work on the PSP, citing perceived problems with Sony as one of the reasons for his departure, but other custom firmware versions continue to be developed or updated. In 2015, a homebrew tool known as Infinity was developed which allows users to permanently install CFW such as LME or PRO on all PSP models. This tool requires firmware 6.60 or 6.61.