I got a Backdoor instaled while in the server  Gehe zur Training: Warchall - The Beginning Challenge

I tried to play this challenge, logged in to the server, and suddenly my computer started having strange behaviour. I made a scan and it found a backdoor

Backdoor:Win32/Sdbot.gen

I demand an explanation.

I highly doubt the sshd on the box is compromised and delivers exploits for putty (assuming you use putty).
I'd more guess your malware was already installed and got active when you connected.

I recommend you re-install your operating system.
If you like you can try to reproduce the infection.

Greetings
gizmore

Someone just recommended to check where you got your ssh client from.
Maybe that's the malware

I feel the biggest problem here is use of windows

I was using SSH Secure Shell. And the malware was installed day 8, when I connected to the server.

Or dloser was at it...again

LOL! I just reversed the polarity of his connection such that I could upload to his computer. n00bs.

Yeah. Perhaps you would be able to do that if the backdoor was still installed.

Why install one if you can install two for the double the price?

Obviously the attacker is one of those above as he already removed the backdoor.