If you want a stable experience without viruses or crashes, consider the legitimate route:

Open GTA SA Mod Loader, select Namaste America, and launch the game. You should now be able to play GTA Namaste America.

If you cannot find a stable version of Namaste America that is truly free and portable, consider these similar mods:

To run the game without a full system installation (making it "portable"): Go to the folder where you extracted or installed the game. Look for the file named gta_sa.exe

On your device, go to Settings > Security, and enable "Unknown Sources" to allow the installation of apps from outside the Google Play Store.