This happens to me any time I access the NA store, and has for a while now (it wasn't an issue until around the time I pre-ordered the Shiva statue). I access it always from the same device, always on the same network, and bam. "Suspicious activity" everytime. It doesn't happen for the Account Management System or the Mogstation - just the NA SE store.

It's really strange how I'll get dinged for "suspicious activity" for this... but I take my laptop to a friend's house or to my parent's house or even to campus and can play the game just fine, despite logging in from a completely different Network/IP.