The game is not broken as such, but I can surely understand that people hate it when their tech is stolen and they feel that they canot do anything against it. If at 60% defense still three techs per turn are stolen that looks like a serious balance issue.
I assume there is a base chance to steal a tech after reaching ultra espionage level, say 10% per turn. Probably the Security rating of a counter spy reduces that chance. A level 1 spy hase a Security rating of 5%. Perhaps its implemented that the resulting chance to steal a tech is (base chance) * (100 - security), in this example 10% * 95% = 9.5%.
If you now have a spy from 10 enemy AIs trying to steal from you every turn, you would lose a tech nearly every turn on average.
That could be balanced by reducing the base chance or by changing the mechanic. I. e. if the security rating would not lower the chance that a tech is stolen, but is the chance an enemy spy is captured and executed then this would make spying much more expensive ...
Perhaps that is moddable somewhere - and if not, it could be made so?