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Due to heavy snowfall I was recently stranded on an airport. Having to do some surfing on my laptop I found an open access point. It offered 30 minutes of free surfing a day. I registered and used up my time.

Then I wanted to see if I could use it again - mostly just for the fun of it. I opened a different browser then before and tried to register again.

It didn't work. The access point recognized me and told me that I'd have to wait another day to get 30 free minutes again. I reconnected again to force a new IP - still the same.

How did it recognize me?

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migrated from stackoverflow.com Dec 31 '10 at 19:45

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It probably remembered your MAC address... (posting as comment because the question is off-topic) –  Thomas Levesque Dec 31 '10 at 14:58
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3 Answers

MAC address.

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I believe Windows also sends the DHCP server your system's hostname or computer name which can also be recorded by the access point. If an access point requires you to go to a web page to login, cookies and other browser-based methods of tracking you can be employed. –  ultrasawblade May 12 '11 at 11:01
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It probably remembers your MAC address. It is also often the case that you won't get a new IP by simply reconnecting, as it will remember the MAC address and IP for a while, and try to give you the same one.

Since you are connecting locally, this is, as far as I see, the only clever solution on their part. Recognizing via IP, cookies or something similar, would just be plain stupid

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Does a website, which at the end of the day it basically was, has any way of accessing the MAC address? Or could it get that from the router in some way :-? –  stephanos Jan 1 '11 at 8:34
    
@stephanos Normal websites don't because your MAC doesn't get sent over the internet, just around the LAN. But since this webserver was on the LAN, and part of the "Hotspot" software, it did have access to that info. –  Bart van Heukelom Dec 13 '11 at 23:07
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It probably stored your Mac Adress. Under most linux distributions you can easily "fake" a new one.

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@Joe:Can you fake it in windows? How? –  Anonymous Dec 31 '10 at 15:21
    
ITYM MAC address (not Mac address). –  Paul R Dec 31 '10 at 15:28
    
@anonymous irongeek.com/i.php?page=security/changemac –  bahamat Dec 31 '10 at 20:36
    
not that i know of, but i am really not into windows. i think as a windows user you shouldnt be required to do so. the use cases of that are off the mainstream –  Joe Hopfgartner Jan 1 '11 at 14:08
    
You might be able to do it by going into the Advanced tab in the Properites page of the wireless network adapter in Device Manager (devmgmt.msc). Also, a good utility I've used before is one called "MacMakeup" (gorlani.com/portal/Home/Projects.aspx). Some wireless adapters don't let you change MAC address though, even with registry edits (mine is one of them :( ). –  ultrasawblade May 12 '11 at 11:07
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