How could Snape be undercover for the Order, when he faced down Quirrell in Book 1?

Snape is supposed to be deep undercover for the Order - but how can that be? When Quirrell had Voldemort on the back of his head - unknown to all but Quirrell - Snape faced him down about allegiances. Voldemort had to have heard, even if Quirrell had not spoken to him about it...

How could Snape be undercover for the Order, when he faced down Quirrell in Book 1?
He explains it to Bellatrix Lestrange in book six when she asks him the same questions. He did not know that Voldemort was with quirrel, and he would not risk his undercover status with Dumbeldore unless he was aware that Voldy was rising again, or his role as double agent would have been jeopardized for nothing. He couldn't let quirrel know that he was working for Voldy unless he knew for sure that quirrel was too. Voldy didn't even let his most loyal death eaters know that Snape was really still with him, he wanted them to wonder in case one of them was a spy for The order or Dumbeldore.
Reply:The Order of the Phoenix was the group that existed when Voldemort was in power, but everyone believed him to be dead after the curse he'd aimed at Harry backfired. After that, there was no need for the Order anymore. When Snape encountered Quirrell, there was no Order. It came into existence once again when it was realized that Lord Voldemort was still alive and attempting to regain power.
Reply:Well, he told Bellatrix and Narcissa in HBP that he couldn't show his true colours because at that time he was convinced the Dark Lord was dead. Besides he couldn't help Quirrel 'cause then Dumbledore would have known that he was really on Voldemort's side, and he couldn't risk his role as double agent. Also, Voldemort wouldn't show himself to Snape because he thouhgt he was gonna trun him in to Dumbledore...
Reply:Voldemort knows what Snape is doing. At that point he still thought Voldy was dead. He is definitley on the bad side, he made an Unbreakable Vow with Narcissa and Dumbledore didn't even know that.
Reply:could Snape's loyalties have changed since book 1?

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