This is an ongoing problem with Netscape, Mozilla and Open Office installers. They use a free compression/archive tool to create their self-extracting installation packages. This tool is constantly being updated to provide better compression, and the newest version is normally used. Since the file is self-extracting, it doesn't matter to Netscape, Mozilla or Open Office if the compression algorithm has changed. The problem is that every time the compression algorithm changes the Sophos anti-virus engine no longer understands how to properly extract the file. This usually results in one or more files triggering a decode/decompress error. Subsequent releases of the anti-virus engine are updated to handle the new formats.