UltraISO is a crippleware application for Microsoft Windows for creating, modifying and converting ISO image files used for optical disc authoring, currently being produced by EZB Systems.

[2] The 'Free Trial' version is limited to ISO images of 300 MB or less, effectively making it Crippleware.

The format uses zlib or bzip2 to compress the data, and may use AES-128,192 or 256 encryption in the CBC mode[4] (note that this provides no integrity protection and is vulnerable to the padding oracle attack[5]).

The file format specification is available publicly on EZB Systems's website.

[4] The format is now supported by third-party applications such as Daemon Tools, Alcohol 120% and CDemu.