Jailbreaking an iPhone for Cydia is not inherently unsafe, but it bypasses or removes some security features of the iOS operating system and is a violation of the software licensing agreement. It can result in software instability, service disruption, decreased battery life and software update failure.
System instability that can result from jailbreaking an iPhone can cause data loss when system or app crashes or freezes occur. The removal or bypass of security features in iOS can leave personal data open to intruders and create vulnerabilities to malware and viruses. Push notifications, data services and data synchronization may suffer from interruptions and inaccuracies as a result of the operating system modifications.