My almost ci site hack

How my almost ci site more than 80 website are hacked in a single day. Notonly the old version of ci new version is also hacked from same persion. I don't know the keyroot from which file it is hacked

There's really no chance that this has anything to do with CI.

It could be anything:
- sql injection
- without file check, the hacker could upload anything. eg. youurl.com/upload/badphpfile.php
- misuse of shell_exec
- backdoors from a former employee
- old plesk, old phpmyadmin
- old server version

Are the 80 sites on the same server?