медвежья услуга

Etymology
From +  - "bear's service". According to, possibly after 's fable about a bear who broke his owner's head trying to kill a fly, in Russia spread thanks to 's fable "The Hermit and the Bear" (Пусты́нник и медве́дь). The moral being "an obliging fool is more dangerous than an enemy."

Noun

 * 1)  disservice, more harm than good an ill turn or injury