highly unlikely, but they can create a patch that installs keyloggers / viruses to trade your skins away. They also can inject viruses into the server / game that everybody will automatically download without even knowing it.
Skial
Metroidz
Virus to trade your skins away? Bollocks
The Emperor
the virus will literally come through your computer screen and go down your penis while you are masturbating then it will suck up all the skin cells from the inside out to be sold on the black market
Even if they could I have nothing of value to steal on my pc, noobs.