What the most harmful thing can malware program started as separate limited user account do if it has access to the X server?
Network and filesystem things are already considered by chroot and netfilter.
It obviously can lock the screen and I will need to switch to other vt and kill it manually. Can it for example disrupt other GUI programs on the same X server (access a root terminal in nearby window)?
I know that it is safer to run it in separate X server, for example, in Xtightvnc or even some virtual machine, but how dangerous is to just run it like other programs?