viodentia  (sometimes written with an uppercase v) is a pseudonym used by the creator of FairUse4WM, a program that removes Microsoft's copy protection technology from Windows Media Video (".WMV") files. These files are used by popular music download sites such as Rhapsody, Yahoo! Music, and Napster.
This copy protection system also has the effect of preventing what would otherwise be claimed as fair use - legitimate owners backing up paid downloads in case of loss or damage to their computer data, or for use in on other devices where legal to do so.
"viodentia" is the pseudonym of one or more individuals who wrote software that would enable users to remove the protection mechanism from their media, thus allowing it to be copied for legal use. Forum posts under the name "viodentia" stated in 2006 that the program was to enable exercise of fair-use rights only, and excluded import of cryptographic data needed for piracy usage.
A lawsuit was later filed by Microsoft, on the basis that FairUse4WM contained proprietary computer code from Microsoft's Windows and/or was a derivative work of Microsoft's Windows Media Format SDK or other Microsoft DRM technologies.
On 22 September 2006, Microsoft filed a federal lawsuit against John Does 1-10 a/k/a "viodentia", hoping to identify the person or persons. An online post by Viodentia contains an implicit defense against Microsoft's allegations of copyright infringement: