Niklas Svensson, a political reporter for the Swedish tabloid, first got hold of the log-in information in March and since then had logged in three times, most recently in August.
“We take this very seriously,” Expressen’s editor Otto Sjöberg said in a press release.
Svensson had not informed his superiors that he had the log-in information, Sjöberg said.
According to Sjöberg, Expressen received the information via other media on Tuesday evening. On Wednesday morning Svensson confirmed that the information was true.