January Jones -- Not Exactly DENYING Liam Hemsworth Affair

January Jones ... the alleged Sienna Miller in the Liam Hemsworth, Miley Cyrus relationship ... finally faced the media about her alleged affair yesterday ... and she didn't exactly deny anything.

The "Mad Men" star arrived to a flock of photogs at LAX and was immediately hit with the questions everyone wants to know -- Did you hook up with Liam? Why were you and Liam photographed together in the back seat of an SUV at the Oscars?

As we previously reported, Miley was spotted out in public this week without her engagement ring ... fueling rumors that she broke things off with Liam because of his alleged affair with Ms. Jones.