'X-Factor' Judges Paula Abdul & Nicole Scherzinger -- Targeted by Death Threats After Voting Off Drew

"X-Factor" hosts Paula Abdul and Nicole Scherzinger voted off the wrong contestant Thursday night -- at least according to several angry Drew Ryniewicz fans ... whose violent threats have Paula and Nicole fearing for their lives.

According to our sources, Paula and Nicole both got the cold shoulder from Simon Cowell after the show ... who was "furious" with their decision. But that's nothing compared to the abusive tweets and Facebook messages they've received. Some of the messages read:

-- "F**K you paula you dumb c**t you voted off the most talented person on your f**king show. i hope you die you DUMB B***H."

-- "I hope you die, you selfish----------"

-- "@NicoleScherzy @paulaabdul go die"