a blog from a guy in an office

I have a Challenge. The challenge is: What's the username.
And I have this image. I'm french and the hint is: Un train peut en cacher un autre.
I don't know how to say that in english. But I'm looking for the username of the "hacker"..

I don't understand what you're asking...

Hello,

With this image, can you tell me what's the username of the boy? Thank you