What does the "under additional review" mean?

I submit a service request sometime ago. Today I got a letter from USCIS saying something like "... we are active processing your case. However, it's under additional review. If you don't hear from us within 6 months, you can call back.

What does the "additional review" mean? Is it a bad thing? I don't see any soft LUD for my case even I got the letter.

所有跟帖： 

• 用"additional review" search一下 -toosad- ♀ (27 bytes) () 05/06/2008 postreply 23:20:05

• nothing, routine excuse for their delay -donkeyroad- ♂ (0 bytes) () 05/07/2008 postreply 06:41:47