Time to update your iDevices to iOS 10.3.2.
Vulnerabilities being patched may lead to arbitrary code execution, allow code to run with root or kernel privileges, or allow an attacker to read restricted memory.
iBooks can be exploited with a specially craft book, which may allow a malicious website to be opened without user permission. This could potentially be used to then exploit Safari and Webkit vulnerabilities, or lead to phishing websites.
Apple iOS 10.3.2 is available for iPhone 5 and later, iPad 4th generation and later, and iPod touch 6th generation and later.