A Homeland Security official said that several federal departments and agencies were experiencing the virus, although the official would only confirm NASA.
"US-CERT has received multiple reports from a number of federal agencies and private sector entities experiencing an e-mail worm," said Homeland Security press secretary Amy Kudwa in a statement.
A spokesman for the Florida Department of Transportation said Thursday that e-mail had been taken down at the agency because of the spam attack. He said six other agencies in Florida had also been hit by the virus. While the Trojan hindered communications, it hadn't had a major impact on operations, he said.
Last Tuesday Adobe systems advised computer security experts that there were vulnerabilities in the Adobe reader software, noting that hackers were looking to actively exploit a recently detected vulnerability. This could explain why the e-mail was being sent in a .pdf format.
ABC News' Jason Ryan, Marisa Bramwell, Lee Ferran and Sidney Wright contributed to this report.