From memory, Triple J radio in Australia were to be the first station worldwide to play the song, being in a pretty good timezone for it. There were then threats from other networks that they would play the song first, so triple J decided to leak it early.
They were under strict embargo not to play it, so they concocted a story if I recall correctly. the radio ad that came out said
"Everyone is waiting to hear the new U2 single, that is released worldwide tomorrow. But we at triple J thought, let's save people some time, so we found it online"
Obviously, as everyone here would know, it wasn't available online, but they said that so that they apparently weren't playing the embargoed version.