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I filled a survey today which states that it can only be done once a month. If I try to do it again, I am not allowed as expected.

I am trying to find out how they know that it is from the same computer.

So far, here is what I tried :

  • I used another computer on the same LAN, and I am allowed to fill the survey. So it is not my IP address.

  • I used the first computer, but with another "private" IP address (192.168.X.X), and I am not allowed to fill the survey again. So it is not the combination of IP address + private IP address.

  • In Chrome, I cleared everything from the past hour and I still can not fill the survey again. So it is not something they put on my computer.

The only option I can think of is my MAC address, but I am not sure it is an information they have access to and I don't really know how to change it (on Ubuntu).

So I am curious as to how can they uniquely identify my computer as a computer which answered the survey.

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I'll be that if you use a different browser, it will work. This is quite often done with fingerprinting like this: Related:… – tjameson Jul 13 '13 at 18:39
I doubt it's the MAC address, since they can be changed trivially. Also, browser having access to the MAC address would be a huge security hole. – AnonymousLurker Jul 13 '13 at 18:49
up vote 2 down vote accepted

What exact method any site uses is hard to say, but there are ways to uniquely identify you based on your browser info. One of the big points of compare, for example, is the installed fonts reported to the web site.

By combining the various things the browser (and its plug-ins) reports, and then comparing them as a whole you become pretty unique.

Check out to get an idea.

Is your browser configuration rare or unique? If so, web sites may be able to track you, even if you limit or disable cookies.

Panopticlick tests your browser to see how unique it is based on the information it will share with sites it visits.

share|improve this answer
This is the answer, as using Firefox allows me to fill the survey again. Changing to a Windows partition on the same computer and using Chrome allows me to participate in the survey too. – Gradient Jul 13 '13 at 18:48
Yeah, I think it's done as a trade off to complaints about doing it by IP(v4) where multiple people are behind NAT routers, using dynamic public IPs, etc. I've also noticed a trend over the last while where contest runners just say straight-out "You can enter up to 10 times", so most casual 'cheating' is allowed, expected, and announced to all contestants in advanced. – Ƭᴇcʜιᴇ007 Jul 13 '13 at 19:56

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