Two attacks on the same day this month and another one last month targeted work stations used by three Nelson staffers -- a key foreign-policy aide, the deputy legislative director and a former Nelson NASA advisor, according to Nelson's staff.

The hackers didn't make off with any classified information, which isn't kept on office computers, a Nelson spokesman said. The cyber-attacks have prompted Nelson, along with Sens. Jay Rockefeller, D-W.Va., and Olympia Snowe, R-Maine, to call for the creation of a permanent national cyber-security czar.

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