CIA director John Brennan has warned Russia has "exceptionally capable and sophisticated" computer capabilities and that the US must be on guard.
When asked in a television interview whether Russia is trying to manipulate the American presidential election, Brennan didn't say.
But he noted that the FBI is investigating the hacking of Democratic National Committee emails, and he cited Moscow's aggressive intelligence collection and its focus on high-tech snooping.
"I think that we have to be very, very wary of what the Russians might be trying to do in terms of collecting information in a cyber realm, as well as what they might want to do with it," he told CBS on the 15th anniversary of the September 11 attacks.
On the terrorism threat, Brennan said the US government is much better now at sharing information.
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He praised Saudi Arabia as "a good example of how foreign intelligence services can work against these terrorist organisations".
On Friday, Congress sent President Barack Obama a bipartisan bill that would allow families of September 11 victims to sue the government of Saudi Arabia.
Fifteen of the 19 hijackers from September 11 were Saudi nationals. The Obama administration has said that if US citizens can take the Saudis to court, then a foreign country could in turn sue the United States.
The White House has indicated Obama would veto the measure.
