Agreed.
Add some feature to allow spy missions to be revealed--otherwise nations act in complete anonymity with no way to discover the culprit of the attacks (or so I understand).
As Paradigm mentioned earlier--allow one of the missions to allow spies to discover the last 10 spying missions a nation has been on (or something of that nature). If not that, some other method of discovery beyond failed missions would be useful. Or something public like fuzzycat mentioned.
Another idea--like the "wars across the globe"/"foreign aid offers across the globe" show "spy missions across the globe": allowing anyone to see which nations have conducted spy missions, however not listing who the mission was carried out against or what that mission was--thus the only method of discovery would be if that mission failed (then only the recipient would know), or if the curious nation sent out their own spy mission to discover such information.