Because the game is no longer sold officially, many websites offer "ISO" files or ROMs for download. Be extremely careful. Sites hosting these files often contain malware or intrusive pop-up ads. If you choose to download game files online, ensure you have a robust antivirus program running.
If you have acquired a game file (ISO), here is how to get it running on your PC using (recommended for stability): ben 10 ultimate alien cosmic destruction game download