Hi Apheirox, out of curiosity, do you have a save game for when this 24k steal happened, and if yes could you please send it to firstname.lastname@example.org? If there are players who build up so much cash we indeed have to cap the maximum amount stolen / sabotaged.
From my played / observed multiplayer matches so far I'm personally quite happy with the effectiveness of espionage and how it plays. However, we definitely have to improve the AI's infiltration skills, lower their infiltration frequency (though they do consider standings and scores for infiltration) and tweak some more numbers.
In general the espionage mechanics are received fairly controversial, will see if we have to do some more radical changes.
4X strategy game from Proxy Studios