[arch-general] Can a ISP modify incoming http traffic to display ads using transparent proxy server ?

[Partha Chowdhury]

My ISP is running a transparent proxy server on port 80 as I found out 
from this thread

http://mailman.archlinux.org/pipermail/arch-general/2011-March/019172.html

Now from last two or three days, I keep getting pop-up ads from a 
particular domain on every website i go to - even on text only websites 
! If i choose another proxy server in firefox , then that does not 
appear on any site. But i normally connect to internet, that specific 
pop-up to a very particular website appears on every single page. If I 
install adblock plus in firefox, then of course no ads are displayed.

So is it possible that my ISP is serving that ad by intercepting 
incoming http traffic ?