In the mid-2000s, digital distribution platforms like Steam did not dominate the market yet. To combat piracy, physical CD/DVD releases used or Serial Numbers. The Metal Slug Collection PC uses SafeDisc or SecuROM (depending on the regional version). During installation, the screen freezes on a dialogue box asking for the "Manual Key" or "Serial Number."
Finding a specific serial number for the (also known as Metal Slug Complete PC Go to product viewer dialog for this item. Numero De Serie De Metal Slug Collection Pc
Disclaimer: Serial numbers provided are for educational archival purposes for legally purchased copies where the original documentation has been lost. We do not condone piracy. Always support SNK and the official releases. In the mid-2000s, digital distribution platforms like Steam