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Groups > comp.lang.java.programmer > #20133

Re: Arranging free trials for online services.

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On 12/3/2012 12:45 PM, Roedy Green wrote:
> I was disturbed when a grammar checking online service wanted my
> credit card before they would even let me see the product.  I
> declined.
>
> Then I started to wonder what such a service could to prevent people
> from getting endless free trials.  Software you install can hide
> something in the registry, but what can online software do?

Send an email and require the user to reply to it. Email is a pretty 
good unique identifier (few people share email addresses nowadays), and 
some analysis on the replied email message can catch some people who are 
using multiple email addresses to try to subvert the free trial. 
Alternatively, a Facebook account seems an increasingly acceptable 
alternative nowadays...

> It would be nice if people had unique ids.  Perhaps someday everyone
> will get a code-signing cert to use as online ID.

We call these online IDs "email addresses." Despite all the constant 
crowing about the death of email, email addresses remain the single most 
common identifier on the internet.

> You could track IP, but a student at a university plugging in anywhere
> to a campus net would get a different IP and many students would get
> the same IP.
>
> You could run some JWS signed code to snoop on the CPU ID, but that
> can be turned off and AMD chips don't have one.

There are several pieces of data which tend to be consistent over short 
periods of time that you can combine for fingerprinting:

List of installed fonts
Number of CPUs
IP address
Browser User-Agent
All other HTTP request headers
Computer's username
Computer's local hostname

Many of these you can get by snooping the request data; the rest can be 
triggered by watchdog plugins (Java applets or Flash objects). If you 
take all of this data and let 1 or 2 pieces change, then you should be 
able to build a sufficiently good unique identifier. The purpose of 
security isn't to make your system unbreakable; it's to make it more 
annoying to break than the person next door.
-- 
Beware of bugs in the above code; I have only proved it correct, not 
tried it. -- Donald E. Knuth

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Thread

Arranging free trials for online services. Roedy Green <see_website@mindprod.com.invalid> - 2012-12-03 10:45 -0800
  Re: Arranging free trials for online services. Roedy Green <see_website@mindprod.com.invalid> - 2012-12-03 10:53 -0800
  Re: Arranging free trials for online services. Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-12-03 14:06 -0600
  Re: Arranging free trials for online services. Arne Vajhøj <arne@vajhoej.dk> - 2012-12-03 22:22 -0500
  Re: Arranging free trials for online services. Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-12-04 16:02 +0100
    Re: Arranging free trials for online services. Roedy Green <see_website@mindprod.com.invalid> - 2012-12-04 18:06 -0800
      Re: Arranging free trials for online services. Lew <lewbloch@gmail.com> - 2012-12-05 10:39 -0800
        Re: Arranging free trials for online services. Roedy Green <see_website@mindprod.com.invalid> - 2012-12-05 14:27 -0800
      Re: Arranging free trials for online services. Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2012-12-06 00:18 +0100
  Re: Arranging free trials for online services. "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-12-04 18:31 +0000
    Re: Arranging free trials for online services. Lew <lewbloch@gmail.com> - 2012-12-04 12:59 -0800
    Re: Arranging free trials for online services. Roedy Green <see_website@mindprod.com.invalid> - 2012-12-04 18:02 -0800
      Re: Arranging free trials for online services. "Chris Uppal" <chris.uppal@metagnostic.REMOVE-THIS.org> - 2012-12-15 12:24 +0000
    Re: Arranging free trials for online services. Gene Wirchenko <genew@telus.net> - 2012-12-13 09:01 -0800
  Re: Arranging free trials for online services. Joshua Cranmer <Pidgeot18@verizon.invalid> - 2012-12-06 11:01 -0600
    Re: Arranging free trials for online services. Leif Roar Moldskred <leifm@dimnakorr.com> - 2012-12-06 11:50 -0600
      Re: Arranging free trials for online services. Lew <lewbloch@gmail.com> - 2012-12-06 10:49 -0800

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