hi

in my security log, I have few "blocked access" with this information : "/zp-core/cron_runner.php".

can you explain what the problem is ?

cron_runner is used for doing the auto backup script. It has built in security checking to insure that no one tries to abuse it. The log entry you are getting is saying that the script is being run without proper authorization. As to why that would be, I do not know.