steam_api.dll file is a core component used by Call of Duty: Modern Warfare 2
Support and Warranty: Using unofficial modifications can void game warranties and make it difficult to receive support from game developers. Players may find themselves unable to get help if they encounter issues.
If you know your antivirus removed the file:
Once restored, Modern Warfare 2 will launch properly, allowing you to relive the glory days of "Rust" 1v1s and the emotional campaign twist of "Shepherd’s betrayal."