> I was wondering if anyone knew a way to block access
> to anonymous proxying sites. Some of our users have
> worked out how to bypass the denied.list and as a 
> result we have no logging as to their surfing
>  activity

Yep, proxies are a _huge_ problem. There are thousands
of them: my personal list exceeded 10,000 a few days
ago, and my blacklist subscription also lists over
10,000. And they keep changing their name every few
days. 

Shady owners can make a small but positive amount of
money from every proxy (apparently through showing
ads). So every Tom Dick and Harry creates one or two
and adds their bit to the giant shell game of "guess
where the proxies are". 

And you're only seeing "most" of it. There are certain
technical tricks that will make a proxy completely
invisible so you won't even realize you're not seeing
the surfing activity history. 

There are even services that will email a user the
"new proxy of the day" every morning. A user opens up
their email, plugs the address into their web browser,
and voila you've been painted as the fool once again. 

Depending on how serious you are about fighting
proxies, you'll need a good AUP (Acceptable Use
Policy), administrative backing, a lot of aspirin, an
hour every day, script writing skills, and a
combination of Squid and DansGuardian. The combination
of Squid and DansGuardian is the only technical
approach I know of that works very well - DansGuardian
pre-scans the _content_ of every site and ultimate
site, so it will block a lot of proxy use even though
you haven't yet configured the exact current name of
the proxy. 

The list on http://proxy.org is the most complete one
I know of. If you can figure out a way to
automatically suck up their entire list _every_day_,
remove duplicates, and add all those to your banned
list, you can stop _much_ (but not anywhere near
_all_) of the illicit activity. 

good luck!


-Chuck Kollars


      
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