In 140 chars or less, “Gauss is a nation state sponsored banking Trojan which carries a warhead of unknown designation”. Besides stealing various kinds of data from infected Windows machines, it also includes an unknown, encrypted payload which is activated on certain specific system configurations.
This Kaspersky blog is in FAQ format with links to HTML & PDF data sheets. In a nutshell, as Kaspsersky digs deeper into malware infections in the mid-east they've again come across something they didn't know or expect existed.