Tornado codes were formerly patented inside the United States of America.<ref>{{harvharvnb|Mitzenmacher|2004}}</ref> Patents US6163870 A (filed Nov 6, 1997) and US 6081909 A (filed Nov 6, 1997) describe Tornado codes, and have expired as of November 6, 2017. Patents US6307487 B1 (filed Feb 5, 1999) and US6320520 B1 (filed Sep 17, 1999) also mention Tornado codes, and have expired as of February 5, 2019, and September 17, 2019, respectively.
== Citations ==
[[Michael Luby]] created the Tornado codes.<ref>{{harvharvnb|Luby|1997}}</ref><ref>{{harvharvnb|Luby|1998}}</ref>
