“As weird as this sounds, some of the newer hacked clients have a feature called CommandBook which allows them to hide commands inside the text of a minecraft book. If you were the admin and clicked on the text in such a modified book you could be running a command such as /op in the worst case.” –SVDragster @ CanaryMod
The text can be absolutely random, it might look like nothing malicious. Worst case for a player you could be giving them access to your home and chests etc.
To my knowledge these books can’t do anything as malicious as acquiring your account information/login details or getting access to anything outside of minecraft. However, it never hurts to be cautious.
So, be careful about reading books given to you by random strangers and don’t click on any fancy links in one no matter what riches they promise you. This is not a built in minecraft feature and it is not a plugin feature we use at Briarcraft.
— A special thanks to SVDragster for sharing this tip at CanaryMod