It's the Steam Client Service. You'll find it in services.msc. It's set to manually run by default.

It's not always running, however. It normally only runs to monitor and update content (since that's what the service is designed to do), usually running on launch, then stopping after it does its initial scan of your local content to see if there are any updates available.

ClientRegistry.blob is a frequent culprit for a variety of Steam-related issues. Exit Steam, delete the ClientRegistry.blob file (located in the main Steam folder) and restart Steam. The blob file will be rebuilt.

assaf181, GTFO from this froum.
If you are getting this error you have a cracked version or cheat ( eg. texture hack or similar )

1. you cannot start the game iw4mp.exe directly from executable if steam service is not running
unless you have a cracked version.

2. if you start the game from shortcut the steam login icon will appear
you log in and have steam service up.

3. if you use some kind of texture hack you will get this message also

The game run fine until 1.0.177 patch while with this patch it was fixed so cracked versions
and many texture hacks have now problem like you have.

so please spear us from BS.

@zck
what did you mean by this:

After update 18/1 its working fine, with no problems.