In #29 The Sickness, the Yeerk Illim tells Cassie:
I know your friend is an Andalite,” (...) “I also know who you are and what you are. All of you,”
Thankfully for the Animorphs, Illim is a member of The Yeerk Peace Movement and thus on their side. However, it still worried me that he knew about them. What about the other "nearly hundred" members Illim spoke about in that book? Did any of these other Peace Movement members also know?
I obviously mean prior to book #49.
See also: How did the Yeerk Peace Movement manage to keep secrets from Visser Three?