How much would it cost to hire a freelance software developer to make a relatively simple application?

It's by the hour, whether it states it that way in the contract, or the developer is experienced enough to be able to estimate a job well. (I'm usually honest with my clients - "If I finish the job sooner than I figured you're going to pay more than you should, if I take longer you'll pay less, so it's a gamble. Paying by the hour won't get you free work, but you'll only pay for what you get." Most of them choose to pay by the hour.) Edit: ANY email program or web browser? If you limit it to any program trying to access ports 25, 80 or 110, it's pretty simple. Just watch those ports and pop up. One version for Windows, one for Mac and one for Linux should cover 99,9% of all computers being used in offices at this time. But so what? It doesn't negate responsibility if you just tell your employees to be careful. It's totally implausible deniability - no court would accept it. If you just mean as a warning and nothing more, sure. If you want someone to write all 3 versions, be prepared to pay about $500-$1,000. Or maybe some high school kid would do it for a couple of hundred. But that's all you get - a popup if one of the ports (outgoing email, web or incoming email) is uses - by any program. If you want ti to cover only web browsers and email programs, but ANY web browser or email program? You're asking for artificial intelligence - which is purely a figment of someone's imagination at this time. (Asimov was a great writer, but his future is still in our future.)