Patent ambush is where a patent holder waits until a technology becomes popular, or until a product developer becomes rich, before launching a patent suit. The patents used in a patent ambush are often called "submarine patents" (although this term's original meaning was only for a certain type of ambush).
This problem exists in all patentable domains but it is particularly unjust in the case of software because the use of software is essential to almost every company, and distribution and development of software is very common (keeping in mind that developing a website is software development).
In some countries, the non-use of a patent could give a defence, known as "laches" or "equitable estoppel", to alleged infringers.
 Old "submarine patents" definition in the USA
Until 1995, the US patent system contained a loophole which allowed patent applicants to keep their applications secret for many years by repeatedly filing modifications. These patents would then "surface" and product developers would be surprised with law suits over patents they never even had the possibility to search for or read. This loophole was closed in 1995 but the effects can still be seen in the term of certain patents, such as US6,185,539. Filed in 1991 (thus still governed by the pre-1995 regime), this patent was only published in 1997 and will only expire in 2017. This is one of the patents which encumbers the MP3 audio format.
 Related pages on en.swpat.org
- Harm to standards
- All businesses have software patent risk
- When is patent abuse illegal?
- GIF - an Internet image file format covered by the LZW algorithm patent
- Patenting around what will become essential
- EU Tests Out Its New 'Patent Ambush' Antitrust Law On Rambus, Aug 2007, techdirt
- EU Accuses Rambus of 'Patent Ambush', Aug 2007, Huffington Post
- The Problem of Software Patents in Standards, Bruce Perens
- Definition of "submarine patent", describing patent ambush, moneyterms
- Court finds Qualcomm guilty of standards abuse, 8 Aug 2007, The Register - the article lacks details - the ruling seems to form a defence against patent ambush, but what was that defence?
- Old-School Submarine Patents, 15 Dec 2010, Patently-O
- Wikipedia:Patent ambush
- Wikipedia:Submarine patent
- Wikipedia:Laches (equity)
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