Even if SS2 were abandonware, "ABANDONWARE" IS ILLEGAL TO DISTRIBUTE.
Bottom line, end of story.
Copyrights are not considered abandoned even if they are no longer enforced, so the software does not enter the public domain just because they are no longer commercially exploited or widely available.
Official word from Irrational: "No, System Shock 2 is not abandonware, please don't warez it"
Consider this the final word from TTLG on the subject of System Shock 2's status. Unless we hear otherwise directly from EA and Irrational, all instances involving the sharing of SS2 will be considered piracy.