Evaluation Copies?

I am about ready to try to sell my software (vb.net, winforms) from a website or a CD.  I would like to provide potential customers a 30-day trial copy, after which the software would cease to work until they purchased a license key from me and pay for it via PayPal.  

I don't have a clue how to go about this, or if its really the best thing to do.  Its just what I have seen other software vendors do and I would like to do it also.

Suggestions, advice, appreciated.

Thanks in advance.
codefingerAsked:
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Aaron TomoskySD-WAN SimplifiedCommented:
The easy way is to Check the date on install, then check every time the program opens.

If your program requires internet anyway you can do a web connection check

You could also build in an algorithm for keys that combine a serial num and a date so people get a key off the website to run. Like avg.
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nepaluzCommented:

If the software is popular, this and the licensing are the more important things. Get them wrong and your pogram will get hacked easily.
1. 30 Day trial
For the trial, keep a note of the installation date on the customer's computer. It is better to have more than two places to store this, checking and comparing each place then comparing whether any has been modified. If so, take the lowest date as the installation date. Also, keep these dates encrypted so that tampering with any number you choose renders the trial ended.
Make sure that these dates are NOT ovewritten by a re-install of your program.
2. The license
As mentioned by aaro... above, get an algorithm combining certain elements of a computer's hardware. NOTE that hard drive serial numbers usually change when the drive is formated (and users tend to do this often), so be careful which hardware items you select as the basis of your algorithm. Store this in several places (not necessarilly hidden from the user), but securely on the user's computer. Do NOT ship your license code with the software, not very wise if it is hacked by one user.
3. PayPal
This is the easy bit. If you already have a PayPal account, the simplest way is creating BuyNow buttons and implementing the PayPal IPN (instant payment notification). This ensure that you can fire off emails containing the license keys as soon as a payment is made.

Good luck in your endeavours. For a first timer, its greatly satisfying when the first purchase is competed. (Somebody pays money for a program that you have written! No better experience that .....)
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Éric MoreauSenior .Net ConsultantCommented:
have a look at http://www.emoreau.com/Entries/Articles/2007/12/Licensing-a-VBNet-application.aspx

it will show you a basic protection for an application in which you can incorporate more advanced features
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