Absolutely right. It's fake. This phrase "useful idiots" (полезные идиоты) is sometimes attributed to Lenin. But you will not be able to find evidence in any of the volumes of the complete works. Joseph Vissarionovich Stalin has nothing to do with this ephimism at all.'Idiots ... but useful idiots.' An opinion generally ascribed to Lenin and/ or Stalin, but I did a bit of research and found that there's no evidence either of them said such a thing (even in Russian), though they may well have thought it. Similar phrases were used by various US journalists and politicians in the inter-war years, and it re-emerged in the now familiar form early in the Cold War.