Shemiras Halashon Halachos
Hilchos Rechilus, chapter 1, section 8 What should one answer? If someone asks, "What did so and so say about me?" If one give a satisfactory answer without lying one should do so, and if not, one may even tell an absolute falsehood. However one may not take a false oath for this purpose - see Be'er Mayim Chayim.
Hilchos Rechilus, chapter 1, section 9 The following two cases are also forbidden: Even if one does not explicitly mention the name of the subject of the rechilus, but through the story the hearer will identify him later. The listener knows the story but not the name of the perpetrator and one hints it to him.