Cron jobs are running but there is nothing in crontab? Have I been hacked?

Question

I have a server that's been running for years now and there are no cron jobs set up. I have not logged in or changed anything in months. Suddenly I started receiving emails that look like this, about once per hour, but not always for some reason:

To: [email protected]
Subject: Cron <[email protected]> [ -x /usr/lib/php5/maxlifetime ] && [ -d /var/lib/php5 ] && find /var/lib/php5/ -depth -mindepth 1 -maxdepth 1 -type f -cmin +$(/usr/lib/php5/maxlifetime) ! -execdir fuser -s {} 2>/dev/null \; -delete

PHP Deprecated:  Comments starting with '#' are deprecated in /etc/php5/cli/conf.d/mhash.ini on line 1 in Unknown on line 0
PHP Warning:  PHP Startup: Unable to load dynamic library '/usr/lib/php5/20090626/mhash.so' - /usr/lib/php5/20090626/mhash.so: cannot open shared object file: No such file or directory in Unknown on line 0

I have no idea what this is talking about. It's bizarre because I did not change anything.

I checked to see if ther eare any cron jobs by running this command while logged in as root:

for user in $(cut -f1 -d: /etc/passwd); do crontab -u $user -l; done

There were none:

no crontab for root
no crontab for daemon
no crontab for bin
no crontab for sys
:
:
etc, for all users

What is going on? How do I stop this? And furthermore, I'm a little concerned that someone broke into the server and changed something, because I didn't touch a single thing.

Any ideas?

Solution

You are assuming cron jobs exist in standard crontabs. Do this:

ls -lR /etc/cron*

Oh, and no... that does NOT mean that you've been hacked!

Comments

[Kasius]

Users can also create their own cron jobs. Check out /var/cron or /var/spool/cron/crontabs.

[UtahJarhead]

Yes, but he already checked the individual users' crontabs (those are what are listed in the directories you listed.)

[Daniel K]

Hi Yanqi, I am afraid I find this answer very confusing. Could you review it for clarity?