Access Restrictions in Squid Proxy

Hi,

I am using squid Version 2.6.STABLE6 server as a Proxy, with Squid-Guard 1.2.1 for restrictions in access. I have defined the following acl in the conf file to block download of certain file types :

acl denied_filetype urlpath_regex "/etc/squid/denied_filetypes.acl"

where the file "/etc/squid/denied_filetypes.acl" contains all the extensions whose downloads are to be blocked. This much is working fine and is blocking all download requests of the desired extensions. This includes extension .exe.

Now I have a list of 5 websites from where I want to allow download of exe files. However, download from all other sites should be blocked. I tried the following 2 rules above the block rule, but they did not work:

1) acl allowed_exe_sites urlpath_regex ^http://download.microsoft.com/.*
http_access allow allowed_exe_sites
acl denied_filetype urlpath_regex "/etc/squid/denied_filetypes.acl"
http_access deny denied_filetype

2) acl denied_filetype urlpath_regex "/etc/squid/denied_filetypes.acl" !allowed_exe_sites

None of the above seems to be working for me. Please help.