Chafetz Chaim, Part One, The Prohibition Against Lashon Hara, Principle 3
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אִסוּר סִפּוּר לָשׁוֹן הָרָע הוּא אֲפִלּוּ אִם אֵינוֹ (ג) מְבָאֵר בְּעֵת הַסִפּוּר אֶת הָאִישׁ שֶׁהוּא מְּדַבֵּר עָלָיו, רַק הוּא מְסַפֵּר סְתָם, וּמִתּוֹךְ עִנְיַן הַסִפּוּר נִשְׁמָע לְהַשּׁוֹמֵעַ עַל אֵיזֶה אִישׁ כִּוֵּן המְסַפֵּר הזֶּה, בִּכְלַל לָשׁוֹן הָרָע הוּא. וְיוֹתֵר מִזֶּה, שֶׁאֲפִלּוּ אִם בְּדִבְרֵי סִפּוּרוֹ לֹא הָיָה (ד) שׁוּם עִנְיַן גְּנַאי כְּלָל, רַק שֶׁעַל יְדֵי דְּבָרָיו נִסְבַּב רָעָה אוֹ גְּנוּת לַחֲבֵרוֹ, וְהַמְסַפֵּר הַזֶּה נִתְכַּוֵּן לָזֶה בְּרַמָּאוּתוֹ, גַּם זֶה בִּכְלַל לָשׁוֹן הָרָע הוּא, וְדָבָר זֶה נִקְרָא בְּפִי חֲזַ"ל בְּשֵׁם לָשׁוֹן הָרָע בְּצִּנְעָא.
The issur of speaking lashon hara obtains even if he does not identify, in speaking, the man that he is speaking about, but he just speaks in general terms, and from what he says the listener can understand which man he is referring to, this is in the category of lashon hara. More that this — even if there were nothing demeaning in his words themselves, but his words could cause harm or ascription of taint to his friend, which the teller intended by his deceit, this, too, is in the category of lashon hara, and is called by Chazal "lashon hara in private."