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How does a trial version determine that is has been installed before, to prevent users from installing it a second time, just like the products of Adobe do?

I'm using Mac OS X Lion.

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Are you asking specifically about Adobe products, and if so, which of those, or are you asking more generally? –  Daniel Beck Jan 31 '12 at 15:53
    
@DanielBeck Ya, I happened met this issue from Adobe Photoshop CS5.1, and it leads me think about the way it uses. :p –  Kjuly Jan 31 '12 at 15:59

4 Answers 4

up vote 4 down vote accepted

It either stores that information somewhere on your disk (slightly misnamed .DS_Store files - to appear inconspicuous - have been used for this), or could even report some hardware information (e.g. MAC address) to the manufacturer if there's an internet connection during trial installation (or both).

That way, the installer can determine that the same product was already installed either using the information from somewhere on your disk, or by contacting some web server.

It depends on the product in question exactly how it works.

You could try to log all disk access by the installer process using e.g. the opensnoop utility to find out what files are accessed, and try to identify the file containing the trial information.

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Thanks Daniel, I'll try to figure it out with your suggestion! :D –  Kjuly Jan 31 '12 at 16:07
    
@Kjuly I don't think you'll get more specific results here, as using the trial version repeatedly might be violating Adobe's licensing agreement. We don't allow Mac OS on non-Apple hardware questions either for a similar reason. –  Daniel Beck Jan 31 '12 at 16:09
    
thanks for your tip, I got it! :) –  Kjuly Jan 31 '12 at 16:13

This is entirely dependent on the program in question, as different programs utilize different methods to check on licensing. For most shareware programs it can be as simple as deleting it's corresponding preference file or Application Support folder. For larger programs like Adobe's Creative Suite of apps it tends to be more complicated. Inevitably it's always the fact that something from the initial install is left over that was used to track how many days are left in the trial (package receipt, dot file, preference, etc.).

A bit maddening when you opened it the day you downloaded it, then don't come back to actually look at the app until a month later.

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Thanks @Chealion, so it's difficult to find out the way(including the files or keys, etc) the app(like Photoshop) uses? So bad.. :( –  Kjuly Jan 31 '12 at 16:01

Not sure there is a simple answer as most vendors keep this info guarded. One way is a registry key that is not in a "normal" location and not easily found. Also could be a hidden file. I am sure there are more.

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OS X has no registry. –  Daniel Beck Jan 31 '12 at 15:56
    
What about the way of Photoshop CS5.1? –  Kjuly Jan 31 '12 at 16:03
    
Thanks Daniel Beck Not a MAC OS user so unaware of that. –  Dave M Jan 31 '12 at 16:07

I think for Photoshop the information is stored on Adobe's servers. I say this because if you were to restore your computer to an old backup, and try to re-install the trial for Photoshop CS, the trial will not work.

I think they use a combination of information to ascertain that you have already used your trial. The MAC address would be the most obvious one to me. It seems too obvious though, so it might be a combination of different information that allows them to identify your computer.

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