Tornado codes arewere formerly patented inside the United States of America.<ref>{{harv|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. Patents are currently valid until 20 years after filing, and sincehave '870expired Aas andof '909February A5, have both expired2019, and theSeptember others17, seem to be predicated on their priority date2019, a case can be made that tornado codes are no longer patent encumberedrespectively.
