You say TD did this because of a hacker? I don't buy that for a second, sorry, something else is up and is not because of what a hacker did sometime ago and how it is currently affecting the pps.
Then I guess you didn't follow the news at the time. A number of brokerages were affected, and it cost them many millions.
And the letter in question is from "some time ago". From the time of the concerns about the hackers.