This article discusses Russian spying activity in Ukraine before the war. For the most part, it looks like Russia was only partially successful.
Disclaimer: It looks like Reuters made significant efforts to find reliable sources, but I have no way to independently verify the content.
>>>Now a Reuters investigation has found that Russia’s success at Chornobyl was no accident, but part of a long-standing Kremlin operation to infiltrate the Ukrainian state with secret agents.
Five people with knowledge of the Kremlin’s preparations said war planners around President Vladimir Putin believed that, aided by these agents, Russia would require only a small military force and a few days to force Ukrainian President Volodymyr Zelenskiy’s administration to quit, flee or capitulate.
Through interviews with dozens of officials in Russia and Ukraine and a review of Ukrainian court documents and statements to investigators, related to a probe into the conduct of people who worked at Chornobyl, Reuters has established that this infiltration reached far deeper than has been publicly acknowledged. The officials interviewed include people inside Russia who were briefed on Moscow’s invasion planning and Ukrainian investigators tasked with tracking down spies. . . .
Though Russia captured Chornobyl, its plan to take power in Kyiv failed. In many cases, the sleeper agents Moscow had installed failed to do their job, according to multiple sources in Russia and Ukraine. Ukraine Security Council Secretary Danilov said the agents and their handlers believed Ukraine was weak, which was “a total misconception.”
People the Kremlin counted on as its proxies in Ukraine overstated their influence in the years leading up to the invasion, said four of the sources with knowledge of the Kremlin’s preparations. The Kremlin relied in its planning on “clowns – they know a little bit, but they always say what the leadership wants to hear because otherwise they won’t get paid,” said one of the four, a person close to the Moscow-backed separatist leadership in eastern Ukraine.<<<
Long before Russia invaded Ukraine, the Kremlin was building a network of secret agents to smooth its path, a Reuters investigation has found.