Some hackers will try to brute force your VPS passwords, its the same with all servers on the internet.
To see if they are:
Login via SSH
cat /var/log/messages | more
and
cat /var/log/secure | more
Look for loads and loads of failed login's
If you find them create a support ticket and we will try help blocking the users via firewalls.
There is no charge for this, even on an unmanaged server.
