Bitser is a free file archiver and backup software application for Microsoft Windows. It can combine multiple files and folders into a single archive file to serve as a backup copy of the original data. It uses data compression to reduce the overall size of files and can provide password protection using encryption. It also has a password manager and a MD5/SHA-1checksum calculator to verify file identity. Bitser was released in January 2009 and has had updates released every few months with new features and bug fixes. It uses 7-zip open source software to perform all of its underlying archiving functions except for version 5 of the RAR file format.