Studio TOMIS

I'm working on a website for a client using Processwire. The client had some questions concerning security that i'm not able to answer so i hope you guys can help me out. In general I was wondering if there are any logs about bug fixes and security updates. Has Processwire ever been hacked? And how will the security be guaranteed in the future? Since the platform is growing I might imagine so will the amount of attacks. For instance one thing I noticed that the .HTACCES file changed between 2.7 and 2.6 was this because of security leaks or because of other reasons.