请帮我看一下USCIS的回复，谢谢！

上个月发了一个I485的service request，今天收到了回信：

Based on your request we researched the status of this 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 do not receive a decision or other notice of action from us within 6 months of this letter, please call customer service at the number provided below.

想请问一下在什么情况下，会需要additional review？多谢！

所有跟帖： 

• 回复：请帮我看一下USCIS的回复，谢谢！ -绿卡神经病- ♂ (171 bytes) () 09/13/2008 postreply 15:15:45

• 典型的对 security check 没过的回复 -frogdumb- ♀ (0 bytes) () 09/15/2008 postreply 08:40:03