This game was called Contra Hard Corps in USA and Japan, but its name was changed to Probotector in Europe (as most Contra titles were). The characters were also changed into robots and certain sequences and gfx was censored/edited (apperantly, the original was too violent for the german audience).
The japanese version is also much easier (you get an unlimited number of credits and more health). There are more differences, but nothing too severe.
About Contra: Hard Corps
2006-06-19 (updated 2007-11-04) #