I run an ecommerce site where users need to sign up in order to make bookings for our transportation services. From time to time, we receive lots of obviously fake user submissions: they all use "123456" as phone number, and come from domains like `asdfemail.com`, `rtotlmail.com`, etc.

Does anyone have any idea of what they are up to? Our site doesn't have any forum, or any place where the user can post content. Are these bots that just look for any user registration page and sign up, in the hope that they can then post spam, or are they looking for something more nefarious and specific to our site?