is codeigniter 3 safe enough to use?

I'd say CodeIgniter 3 is safer. If adds the new Encryption library, changes the way sessions are stored, and has an enhanced form validation class. The database classes and most of the other classes are from CI2, yet scrutinized and continually developed for security and performance. Many thousands of eyes and users have tested the code by now.

Now, none of that matters if you make stupid mistakes. Regardless of the framework you choose, if you don't know PHP and know about common PHP security issues, you're destined to create an application with security issues. CodeIgniter is not a magician.

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