As reported in The Reg, the Russian stock exchange (RTS) was forced to stop trading between 13:15 and 14:20 GMT on Feb 2nd. The problem was that an infected computer on their network was generating too much traffic, overloading their routers. (There are reports that this may have been an intentional attack.)
The fix was to turn off the infected machine.
I'm sure there is a pun in there about post-Soviet Russia, viruses and stocks.