How do I enforce an expiration date for a trial install of my software?

Question

I need to offer a trial period for my custom software. I have a 64-bit C# app, which uses 64-bit, multi-processor support DLLs. Other utilities to be included are written in C++

Answer 1

Why not just use the time from an internet source, like www.time.gov? You could fold in a C++ Qt app and use their QtWebKit library, http://doc.qt.nokia.com/4.7/qtwebkit.html, to download the time. (I've never in fact done anything like this, but looking at the documentation it looks promising.) The first time the program runs, you create a little file with a timestamp, or, for even more security, write the timestamp into a program-essential dll and recompile it. This gets checked every time the program is run. If you they're not connected to the internet you warn them a few times but eventually abort the load.

Another variation on this, used by a lot of software packages I think, is that you store the date the user starts using your software on your server. Recompile the program for each user (you might be able to script this) with a user-specific code, and the program checks itself against the date stored on the server every time it is loaded.