blocking different sites... but is also blocks the words in a searchstring

To block some site I have entered the following rules in squid.conf:

acl blockedsites url_regex "/etc/squid/block.txt"
acl unblockedsites url_regex "/etc/squid/unblock.txt"
http_access deny blockedsites
http_access allow unblockedsites all

But is someone type porn (a word in block.txt) as searchstring at eg. altavista
the message appears that this url is blocked.
The only thing the person would do is searching for that word and maybe read
some articles in a newpaper archive.
So what I want is blocking URL's not typing words.
What did I do wrong????

Your's sincerly,

R. Boussen
Systemadministrator
Audax A&I B.V.
the Netherlands

business address:
email: R.Boussen@Audax.nl
tel. : +31 161 457847
fax. : +31 161 457777

private address:
Roger@Boussen.demon.nl
Received on Wed Feb 02 2000 - 10:57:54 MST