Hackers have probed the voting systems of many U.S. states but there is no sign that they have manipulated any voting data, Homeland Security Secretary Jeh Johnson said on Saturday. National security officials are investigating a number of possible leads suggesting that cyber-criminals are trying to influence the Nov. 8 presidential election, including by hacking into systems run by the Democratic National Committee.

"We urge states to take full advantage of the robust public and private sector resources available to them to ensure that their network infrastructure is secure from attack. In addition, the Department of Homeland Security stands ready to provide cybersecurity assistance to those states that choose to request it," said U.S. homeland Security secretary Johnson about the election systems.

In recent months, malicious cyber actors have been scanning a large number of state systems, which could be a preamble to attempted intrusions. In a few cases, the U.S. authorities have determined that malicious actors gained access to state voting-related systems. However, they are not aware at this time of any manipulation of data.