I am sure there are flags that can be tripped by creating a bunch of accounts from the same IP. However, I want to say that I did create about 30 accounts in February of this year within a 2 week period from 3 different IP's and that was to get around the daily limit more than I was trying to circumvent any security measures. The biggest thing I think I did to help keep these accounts from being flagged for security is that I didn't level them right away. It was after Anniversary started that I leveled them to 20 to do the Drunkard Stein quest, then it wasn't until the July 4th weekend, with the bonus experience that I leveled them all. I understand that when leveling a group, that isn't ideal to wait, and I don't think you have to wait as long as I did then.
Let me give my most recent example. A couple of months ago, I created 4 accounts and only 4 from a single IP. I created them on Thursday, leveled them to 85 by Sunday and on Monday I got the 2 factor message about suspicious activity and increasing security on the account. Two days later, I created 4 more accounts from the same IP, though different from the first 4 accounts. I didn't level them until this past weekend and did almost exactly the same thing in leveling them to 85 over the weekend. It is now Friday, I have continued to level them during this bonus and still have not been asked to increase the security of the accounts.
Maybe I am way off base and I am sure others will have different experiences, but hoping this information may help.