I read a Hadeeth where the Prophet, sallallaahu alayhi wa sallam, was asked about hyena (an animal who is known to be a scavenger) and he said that it was a game? Is this an authentic Hadeeth? If yes are we allowed to eat it?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

The narration you are asking about is reported in book of Imaam At-Tirmithi from Abu 'Ammaar that he asked Jaabir "Is hyena considered as game?" He said, "Yes." He asked, "Can I eat it?" He said, "Yes." He asked, "Have you heard this from Allah's Messenger ?" He said, "Yes." [Ahmad, At-Tirmithi] Another narration added: "If one hunts hyena in the state of Ihram he has to slaughter a ram." [Abu Daawood and Ibn Maajah]

Imaams Ash-Shaafi'ee, Ahmad, Is-Haaq are of the opinion that eating hyena is lawful. Imaam Ash-Shaafi'ee said: 'People have been eating and selling it (hyena) between As-Safah and Al-Marwah without any objection because Arabs like it and find it delicious.'

Imaam Abu Haneefah considered it forbidden. He cited the following narration as basis for his saying. The Prophet said: "Eating every beast of prey that has a canine tooth is forbidden." [Al-Bukhari and Muslim]

The first opinion is preponderant since the narration that allows eating hyena particularly addressed the issue, while the other narration is general. So, it is preferred over other one.

Allaah knows best.