It is legal to use unlock codes for unlimited play of HP games as long as you have purchased the code and it legitimately belongs to you. It is not legal to use unlock codes that you do not own and for which the company has not been rightfully compensated.
HP Games, the version of WildTangent Games specifically branded for Hewlett-Packard, comes pre-installed on HP computers. It features an extensive selection of games spanning a wide variety of categories, all of which include a one-time free trial when the game is first accessed.
After that initial no-cost period, an unlock code may be purchased to enable non-stop play of that particular title. Alternatively, players may also purchase a set amount of "WildCoins," which allow game play of any available WildTangent game in exchange for a certain amount of coins.