The fact is you probably want to block a lot more than Atdmt.com. I recommend you get the hosts file from
WinHelp2002 MVPS Hosts and use that; you will be amazed by how much "crap" you never see again. (Read on before fetching MVPS Hosts yourself)
And a good way to manage your hosts file is with a program called
HostsMan which is in our
Freeware DB. With HostsMan you can easily turn off the blocking if you visit a site like ABC.Com which requires you not to block ads in order to watch their TV shows; simply find the HostsMan icon in the system tray, right-click, and uncheck "enable hosts" (simply check it again to turn it back on).
HostsMan saves all that time dealing with the hidden and system attributes of the hosts file and the time to copy an clear file back and forth when you need to disable blocking.
HostsMan even has an option (Ctrl+U) to simply go get the MVPS Hosts entries and merge them (these are updated approximately every quarter so update periodically). You may also have hosts from other sources. For example, if you use Spybot Search and Destroy, it will put entries in your Hosts File and when you merge those with MVPS Hosts you should use another great HostsMan option ... I have over 30,000 entries, so sorting and removal of duplicates can greatly improve URL processing time.
Also, one thing amaltom mentioned is setting it to 127.0.0.1, it is actually more efficient to use 0.0.0.0. 127.0.0.1 tells it to look locally, 0.0.0.0 tells it it's a dead link and it can stop looking immediately; the difference is probably thousands of a second but if a webpage has a thousand ads that's a second you don't waste. There is even another option in HostsMan to change all 127.0.0.1 entries to 0.0.0.0, after which you should run remove duplicates and then run optimize.