Security concerning Tor, BitTorrent and Firewall

[a a <werner12345@xxxxxxxxxxx>]

USING:

Tor & Privoxy & Vidalia bundle 0.1.1.26
Windows XP Home
µTorrent
3com firewall

HAPPENINGS:

I am using Tor behind a 3com firewall, in connection with µTorrent.
Before using Tor I -naturally, having not opened any ports on the
firewall- experienced low connection (up&down) rates in µTorrent. However,
after installing the Tor bundle and configuring µTorrent for use with the
Tor proxy server (as described at
http://wiki.noreply.org/noreply/TheOnionRouter/TorifyHOWTO#head-0d047b05e9b
93c23cec9198550816a114012bde0), I suddenly experienced connection speeds
which would equal those, had I used a normal port forward on my firewall.

QUESTIONS:

Firstly, how does this work?

Secondly -on account of a port forward always being a security risk- Is
this a similar security risk?

And lastly, if it is indeed a security risk (no matter how small), does
this apply to other programs than BitTorrent clients, using the Tor proxy
server?
__________

I first inquired with the Privoxy about this issue (presuming that it 
was related to Privoxy) and I recieved the following response: 
> --- Date: 2007-02-19 13:17 Sender: fabiankeil </users/fabiankeil/> --- 
> Are you sure that your provider doesn't throttle BitTorrent traffic? 
> By using Tor you prevent your ISP from knowing which services (other 
> than Tor itself) you're using and this could explain why using Tor 
> speeds up your BitTorrent traffic (it's no longer rate limited by your 
> ISP). Privoxy itself is unlikely to have anything to do with it and I 
> don't think port forwarding has anything to do with it either, but I'm 
> not familiar with BitTorrent. The short answer to your last questions 
> is "No", but as it has nothing to do with Privoxy you should checkout 
> the Tor documentation for details and ask again on the or-talk mailing 
> list if you have further questions.
I am fairly certain that my ISP is not the issue here, so I remain 
puzzled... And I've so far not found any answers in the Tor documentation.

Anybody got something on this?

- Arand