"We've just changed our procedure to be less transparent," said the Briton in Monaco.
"There were some comments (by Marko) about Ferrari spying on us which I think have been misinterpreted," said Horner.
For sure, we cannot intercept the communications of other teams
"I don't know whether mechanics were putting their hands in their pockets at the wrong time or somebody was picking a tyre up," he added, speculating about how Ferrari managed to know about the timing of the stops.
"I think that is probably (the) most likely (explanation), which is absolutely allowed."
He acknowledged that "hacking" into a rival team's radio system "would be very difficult".
Said Ferrari's Felipe Massa: "For sure, we cannot intercept the communications of other teams."