If I remember correctly it was a Soviet/East German propoganda play that gave rise to the falsehood that the Pope was silent about the Jews during WWII. This was because the Church, which was seen as the greatest enemy of communism, had to have her credibility and moral authority destroyed so people would not listen to her about the evils of communism. Sound familiar?
Yes, it sounds very familiar. FReepers have posted the details several times. It's interesting that the sources used to attack Pope Pius tend to be atheists and Communists.