As presidential candidates tack and weave through their primary races and toward their upcoming party conventions, the eyes of voters—and indeed, the eyes of the world—are on them. But a few groups are watching especially closely.

Hackers have been spying on candidates and their campaigns, said James Clapper, the director of national intelligence, during an event at the Bipartisan Policy Center on Wednesday. And the hackers may be on foreign governments’ payroll.

The FBI and the Department of Homeland Security have met with campaigns to educate them about the threats and help counter them. There have already been signs of hacking attempts, Clapper said, and “we’ll probably have more.”

Hackers and spies have targeted campaigns since at least 2008. Earlier this month, the Office of the Director of National Security declassified a slide deck that was presented to the Obama Administration shortly after he was first elected, entitled “How to Use the Intelligence Community.” That deck included a warning that foreign intelligence services “have been tracking this election cycle like no other.”