Windows SmartScreen prevented an unrecognized app

Real-time antivirus scanning is one of the most common causes of Smartscreen Warning on Windows that completely disappears when antivirus is disabled. Build tools, package managers, and development servers create and delete many small files rapidly — exactly the pattern that triggers antivirus false positives and file locking. Windows Defender's real-time protection scans each file as it is created, holding an exclusive lock briefly. When npm, cargo, or gradle create thousands of files in quick succession, Defender's lock causes Smartscreen Warning file access errors. The targeted fix: add exclusions for development directories in Windows Security → Virus & threat protection → Manage settings → Add or remove exclusions. Exclude the entire project directory, node_modules, %APPDATA% pm, and %APPDATA% pm-cache. Third-party antivirus (Malwarebytes, Norton, Kaspersky) have similar exclusion mechanisms. Do not disable real-time protection entirely — use targeted exclusions for development directories only. Also check Windows Defender Firewall for blocking outbound connections from Node.js or Python, which causes network errors resembling Smartscreen Warning.