Account Guard is one of the worst types of 'account security' imaginable.
It doesn't address the type of hack that actually happened to Cryptic's database in the past. Like Windows Vista's UAC, it repeatedly annoys the customer and gives a false sense of security while not actually making the account more secure. And the ten IP address limit in no way makes an account more secure, but it does present a significant risk of permanently locking a paying customer out of their game account if they move or even if their ISP simply changes their dynamic IP address range.
A security key system, like several professionally made MMOs have, is far more secure than this cheap Account Guard. But that would require spending money to implement, and it would also require that someone at PWE have a basic level of competence with computers that the recent forum transition has proven that they simply do not have.