launch app

What's the best way to send an executable to a client desktop in PHP? I'm doing a project where we need to check and see which files need to be updated on a client-desktop. The idea is for a user to visit the website, an executable launches, checks the files on the drive, and then sends the data back to the website. It's all on the up and up - I'm not trying to do anything bad to the user. The site is designed to maintain a product that they're purchasing from us. Screens will explain what's going on. I also believe the browser will display something - not completely sure how to trigger this, but I think it's something to do with having executables "signed" - I'd appreciate if you have any advice on how to do this also. Thanks, Ed