They know I'm using a proxy(Tor)...but how?

[dr._no at cool.ms]

Hi,

> Tor exitnodes are found on several blacklists where these public  
> proxy's are also found on. It seems very likely to me that they just  
> check the IP your connection is originating from on several blacklists..

yes, but this method has two bugs:
a) Tor exitnodes with dynamic IPs do change their IP so that they usually can
not be found on these lists. And someone who is using such an IP some time
later gets blocked!
b) When the output traffic (to port 80) is forwarded to another IP, e. g. with a
transparent proxy which has another proxy as parent proxy, the parent proxy
and not the Tor exitnode gets blacklistet!
I can see this with my Tor exitnode at home: Directly i can connect every page
which blocks TOR and the proxy of my provider, which is no Tor exitnode, gets 
blocked because that proxy, which is neigther open nor anonymizing, is on about
half of the blacklists.

Regards,

Rolf