If a different move becomes best at very high search depths at the root, re-searches to determine its exact score and the new principal variation are done faster due to a reduced search depth, presumably in conjunction with extensions along the PV. According to its author, Houdini 3 applies a accelerated principal variation search, also dubbed 'Smart' Fail-High.
Houdini 3, released in October 2012, has further improved by more than 50 Elo points. Houdini 1.5a remains available as a free download.
Houdini 2, released in September 2011, is commercial and bundled with a number of ChessOK products, such as Aquarium, Chess Assistant, and since December 2011, Chess King. In January 2011, Houdini 1.5 was leading Ingo Bauer's IPON rating list. A chess engine by Robert Houdart, which appeared in 2010 as closed source engine, free for non-commercial use.
