to XIAOBAITU I140 security check HELP HELP!!

I was told by VSC that my I140 is under security check. Does anyone know what the difference is between this and I485 security check? I have been waiting for response in 6 months already after RFE. VSC said they have no other information except waiting for the check result. Any way to check the status and how long it might take, 1,2,3,4,5 years or ..?? Appreciate your advice!