Recently, one of the HL2Files.com members here, alerted me of a pirated warez version of Half-Life 2, apparently released via the Bittorent network. I immediately, forwarded this to Gabe Newell of VALVe Software. A couple of hours later, Gabe replied with the following:
We're running a bit of an experiment. We're keeping track of the accounts that do this and will be shutting them off.

Here's how:

net_start
sv_lan 0
deathmatch 1
maxplayers (whatever you want)
map (mapname)
restart

It will add you to the master server and it works.