I know what I call it.

Hover over all icons, right click, and delete. Or go into the control panel and delete from there.

I suggest both...as a start. Then a search to find the additional places it has crawled into and delete from there. Then a good registry cleaner.

We'll see if that's enough to get it.

Lots of programs leave files behind after an uninstall because they contain user data that a user may not want deleted (although it's considered good form for the uninstaller to ask the user if they want them deleted). Also, sometimes programs that auto-update download updates to the file system that are actually full installers for the app. Are you sure you're not seeing this situation and mistaking it for malware-like behavior?

*Yawn*

First, there's already a thread for Steam discussion. Secondly, see any other program that alters the Windows registry. Or, you know, you could just use Linux and never have to worry about the registry ever again.

As to your "problem", you could just follow the directions Valve gives for https://support.steampowered.com/kb_article.php?ref=9609-OBMP-2526. But complaining about it probably felt better.

Hhm, maybe a Trojan? they pose as one program and open a back door to allow other malicious programs to install themselves.

of course nothing can install on your PC unless you allow it to, that's what i was taught in college

So, like Windows, then?

Then you were taught very wrong. See any number of computer worms that can infect systems without user intervention, dating all the way back to http://en.wikipedia.org/wiki/Morris_worm.

what exactly is meant to be discussed in this thread?