It depends on what "it" refers to. If "it" refers to no one except Durachinsky knowing how it spread, then yes, "it" was solved by the FBI a long time ago. If "

It depends on what "it" refers to. If "it" refers to no one except Durachinsky knowing how it spread, then yes, "it" was solved by the FBI a long time ago. If "it" refers to no one outside the FBI and Durachinsky knowing how it spread, then "it" was solved earlier "today" by Wardle.