"U.S. officials and security specialists are warning that Russian hackers may respond to new Western sanctions by attacking the computer networks of U.S. banks and other companies...Cybersecurity specialists consider Russian hackers among the world’s best at infiltrating networks and say there’s evidence that they already have inserted malicious software on computers in the U.S."
http://mobile.bloomberg.com/news/2014-04-26/officials-say-russian-hackers-may-retaliate-for-sanctions.html