请教小白兔，射线，两分钱以及其他高手: “additional review” 指的

I485 EB1b(OR) 05/2005 VSC
1st FP: 06/2005

07/2006 打电话去USICS查询进展，被告知“security checks remain pending”。01/2007再次打电话查询。03/13/2007 2nd FP。昨天收到VSC的来信：“on 01/03/2007 you contacted us about your case………….We are actively processing this case. However, we have to perform additional review on this case and this has caused a longer processing time. If you don’t receive a decision or other notice of action from us within 6 months of this letter, please call customer services.”

“additional review” 指的是什么东东？信中未提security check, 是否意味着我的name check 已经clear啦？难道我还要再等6个月？我和我太太的I485一直在VSC,没有被转移。

谢谢先