squid acl and attachments blocking

["Gytis@gw" <gytis@aura.msrautas.lt>]

hi all.

So i got tired of all viruses, antivirus on my email helps, but not much ,
cause there are lot of webmail sites. So i want to block some attachments
from them.
I have read the squid documentation and got this far :
acl badURL url_regex -i testsite.*\.vbs$ testsite.*\com$ testsite.*\scr$
testsite.*\pif$
testsite.*\exe$
http_access deny badURL

and everything works fine if i have a site like :
www.testsite/path/to/file/file.scr i get a nice access denied page, and in
access log i see line :

1059111048.385      1 xxx.xxx.xxx.xxx TCP_DENIED/403 1079 GET
http://www.testsite/kelias/iki/failo/failas.scr - NONE/- -

this is what i want. But i have a webmail wich handles attachments like this
:
http://www.othersite/index.html?screen=AttachmentServer&attachment-id=3091000000180264329

so it doesn't block anything, and in log i see :

1059111360.256    719 xxx.xxx.xxx.xxx TCP_MISS/200 10916 GET
http://www.othersite/index.html? - DIRECT/xxx.xxx.xxx.xxx
application/octet-stream


What can i do then ? I just need to block some attachments from some webmail
sites, not all attachments