Metal Slug 4 was released in March 2002. Developed by Mega Enterprise, a South Korean company.
Mega Enterprise got Copyright of SNK's games for South Korea in 1999. In 2006, the South Korean police had an claim for arrest warrant against Lee Sang Min, president of Mega Enterprise. Lee Sang Min escaped in China, abandoning its company (only a few people occupying the office). Mega Enterprise went out of business soon after.
A hack of this game is known as "Metal Slug 4 Plus