It is as secure as it needs to be, there are some flaws & attacks to get access to your data so the usual rules apply.
If someone has physical access they can probably read your data if they are smart enough, loss/ theft is the easiest way to loose data, especially with no PIN/ password on the phone.
Malicious attacks can be avoided by…
Taking care when browsing & using mail.
Don't connect to every wifi access point you find, it is possible the access point (or someone connected) is set up to collect data you are sending.
You should also be concerned if it looks like your own network is available somewhere away from home.
Turn Wifi & Bluetooth off when you are not using them. Password protect your home wifi too.
Don't install every app you find on the store, it is possible for apps to send your data elsewhere, but Apple try to stop invalid reasons in the approval process.
Use multiple passwords for different services, and be don't just enter them when any old app or website asks for them.
Avoid keeping Credit Card details & passwords etc on the phone.
Apply software updates promptly. Apple released a fix after a few weeks for the recent jailbreakme.com hack that could get root access on the phone. Apple can be really slow to fix bugs but you are better off with the fixes than without.
If you are really concerned about your data don't forget it is also on your Mac too & inside any Time Machine backups. A decent account password is a good start because the keychain uses it by default.
Also use the 'encrypted backup' option in iTunes and use File Vault to protect the Address Book, Calendar, email & Home folder contents.
I hope I haven't given you nightmares :)
Re:co
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