Startup Sentinel is a free tool which helps you take control over your Windows startup programs.

Run the program and it monitors the main startup locations. If an installer tries to add itself without your permission, Startup Sentinel detects this and displays a warning.

If you don't want the new program to run when Windows starts, clicking "Remove" deletes it right away (the startup reference, not the program itself).

If something keeps trying to run at startup, add it to the blacklist and Startup Sentinel will automatically block it in future.

Alternatively, add a known safe program to the whitelist and Startup Sentinel won't prompt you about it again.