The .zip compression format has known remarkable stability and compatibility for many years, but that may soon change. PKWare and WinZip, makers of competing compression and encryption products, are fighting over the .zip standard--which means that .zip archive files created by one program may not be accessible by the other. Both companies recently changed their implementations of the .zip format. In May, WinZip released a beta version of WinZip 9 that alters the .zip format. PKWare made its changes earlier, but recently posted specifications detailing its changes to the format. Read more: PC World.