It was first announced in 2010, and was last showed to the public at E3 2011. Then, amid multiple rumors concerning major project shifts, it essentially disappeared.
The XCOM first-person shooter, an apparent reboot of the classic franchise by 2K Marin, has been delayed multiple times. The latest issue (as spotted by Digital Trends ) is that the official site for the game in question has been taken offline. Furthermore, any official videos released to YouTube have been now marked as private.
It could be that the 1960s-themed shooter is being re-branded, as Take-Two Interactive has most recently said the game would still release between April 2013 and May 2014. The game might now be called "The Bureau," as evidenced by new registered domains, and some have claimed the title will emerge as a third-person shooter rather than a FPS. Either way, we're perfectly willing to wait; what we saw a few years back wasn't even remotely impressive, if I remember correctly.
If you want a great XCOM experience now, just pick up the award-winning XCOM: Enemy Unknown .