Block ad sites with Hosts file - not working ?

I have a customized hosts file with sites as adultfriendfinder.com,
doubleclick.com, fling.com .... and the like included in it.
However, I find that embedded ads as well as occasional popups from these
(and other sites included in the hosts file) appear both in Internet
Explorer as well as Firefox!
The syntax used is correct AFAIK. For example:
127.0.0.1 doubleclick.com
Is there something I am overlooking?
TIA
Rubicon
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Rubicon wrote:

> I have a customized hosts file with sites as adultfriendfinder.com,
> doubleclick.com, fling.com .... and the like included in it.

No, you don't. If you have a hosts file, it has a list of *hostnames*,
not domains. The hosts file is only usable if a fully qualified domain
name is specified, and that includes the hostname. You can't block on
domains using the hosts file. You can only block (redirect) based on
hostnames. That is why, for example, ther are over 50 entries for the
Doubleclick domain to block ads from there, and that still does not
guarantee that all ads from Doubleclick will get blocked. They could
add another host as their ad server. They could rename a host. They
could use a boundary host that accepts any hostname so you will never
have a complete list (because you cannot specify a domain, only a host,
and you cannot list an infinite number of hosts). The site could use a
server-side script that decides from where to retrieve the ad but the
hostname or ad source changes all the time and is a host that isn't in
your hosts file. They can stream the data so your web browser hasn't a
clue what is the source host for the content. They could use Flash to
hide the source.

> However, I find that embedded ads as well as occasional popups from these
> (and other sites included in the hosts file) appear both in Internet
> Explorer as well as Firefox!
> The syntax used is correct AFAIK. For example:
> 127.0.0.1 doubleclick.com

No, that is NOT correct syntax. Domains cannot be specified. HOSTS, as
the file is named, must be specified.

> Is there something I am overlooking?

Yep, and already mentioned above. Look at the MVPS hosts file that you
can download. You won't see the doubleclick.net and doubleclick.com
domains listed. You will see hosts on those domains listed, something
like <hostname>.doubleclick.com, and you'll see dozens of them because
lots of hosts are used by that ad service, they change to different
hosts, they change their hosts names, and have other ways of hiding the
ad source.

If you want to block on domains, get a firewall with that feature, or
incorporate an add-on into your web browser with that features (IE7Pro
has that but obviously only for IE). You could also stop using your
ISP's DNS server and use one that lets you block domains, like OpenDNS.
You configure your TCP parameters to use OpenDNS and in your account
there you add domains to a block list; however, I believe you must run
their DNS Updater client (I use the one from DynDNS since I also use
that service to equate my dynamic IP address to an IP Name for easy
access to my host from somewhere else, like from work) to report your
current IP address to your OpenDNS account so they know for which host
your account's config is to be applied.