It appears another invasion may be imminent, Commander. A rather large set of new achievements for the PC version of the game seem to suggest that more content is on the way for XCOM: Enemy Unknown.

The Global Gameplay Stats on XCOM's Steam page (via Polygon) lists 30 blank achievement entries, likely to be filled in once an update hits.

2K recently confirmed something XCOM-related is on the way, and a ratings board leak implied it will be called "XCOM: Enemy Within." We haven't been sure if that would be a true sequel or merely an expansion, but these achievements give more weight to the latter possibility.

Shacknews has contacted 2K and will update as more information becomes available.