When applying online for ANY immigration matter, you should always make sure that your application is being filled out at the official USCIS web site. There are more and more web sites purporting that they conduct legitimate immigration business, but a lot of them only mimic the USCIS pages, in order to coax users into believing they are paying the fees needed for their application, when in fact, they will pay the scammer and never have an application filed in the first place.
Avoid being a victim of this type of fraud by always checking the address of the web site where you are filing the application. Study the picture posted here with great attention. To date, this is the address (URL) where the online form filing with USCIS (eFile) is conducted. As a rule of thumb, do not attempt to file anything online without consulting with your attorney first!