Punkbuster starts on a fresh Steam install with no games downloaded. It's bundled with Steam, it seems... :|

Punkbuster keeps something running, even when you're not playing the Punkbuster related game anymore. I had that with BF3. or BC2, not sure anymore.

It isn't bundled with Steam btw, unless you start up a Steamgame that uses it.

Yes, Steam would be a lot more palatable to me if you had the option of ~permanent~ offline mode, as in Steam will secretly do an online check once you start up your computer, then go into offline mode, without alerting the player in any way. Valve are obviously still very pro-DRM, otherwise you'd see them start in that direction, disabling the "Would you like to start in offline mode" everytime you start your computer. Even removing Steamworks entirely for playing games except a one-time activation when you buy the game.

Steam fanboys always say how it's convenient and the DRM isn't obtrusive, but fact is that Steam IS obtrusive, afaik UPlay only has one-time activations via the client. The very idea that you have to have a client running to play a game you paid for and own... is utterly repulsive.

Just decided to go with an unconfirmed post like it was fact huh. How do you explain people who actually don't have internet being able st ay offline for long periods of time then?

Good news for you then - it does that now if you are not connected.

sigh. Silently starting Steam in offline mode without any warning when not online - Check.

Until yesterday I had assumed using the Windows firewall to block steam.exe would be sufficient to truly keep the client from communicating with Valve, but after Trilarion wrote about Steam updating in offline mode I dug around a bit and I don't think that's true anymore.

If I block steam.exe and put the client offline, then click on "Steam" in the top left corner and then on "Check for Steam Client Updates" I get the message "Your Steam client is already up-to-date". Sounds like it did check for updates, but maybe they just forgot to put in an error message if the client can't connect, right?

So I installed Wireshark to monitor my network connections. Now, this is the first time I have used this program and I don't understand 75% of the information I get. Hence there is the possibility I misunderstand something. But according to the log, when I click "Check for Steam Client Updates" a query is send to something identified as "media.steampowered.com". I then instantly get a query response from CNAME "valve.vo.llnwd.net".
Sounds very much like communication between my local client and Valve to me and if this happens after I prompt it I wouldn't be surprised if the client did this without my prompt at least once in a while.

TLDR: Offline mode + Windows firewall blocking steam.exe is seemingly not enough to
keep that sneaky thing quiet. I'll test if different firewall settings make a difference and post here if they do.

Basic Firewall block in Windows is incoming only as far as I know, you'll have to add rules to prevent outgoing traffic. And I'm still confused about the public vs Home thing :)

Public vs Home deals with your shares mostly. In a home network, if your documents, pictures and videos are shared, they are viewable from all other computers in the home network. In a public one, even if they are shared, they shouldn't be viewable. Same for printers as I recall.

Nah, I've specified an outbound rule for steam.exe and all obvious client functionality like the store and community tabs stopped working after that.

OK, so maybe it was installed by something else? I don't play multiplayer games but I'll look into that.

Cool, keep us posted. I'm interested to see what you come up with.

You can see a list of games using PunkBuster on its Wikipedia article. Games using PunkBuster will install it unless the game's multiplayer has a separate listing in the Steam library (in which case PunkBuster would only be installed if you install the multiplayer).

To block steam I had to switch on blocking of outbound connections by default and explicitly allow the programs that I wanted to access the internet. It's possible different versions of Windows do different things.

Steam updates are handled by the Steam Client Service (SteamService.exe). You would need to block that one too.