It looks like one or a few different people are searching for a way into our community, using a variation of the same usernames with different email addresses. 

Invisionzone *appears* to be holding the line, but should I be worried?

Thank you in advance for any help or suggestions.

You will receive individuals and bots attempting to login to your community throughout the lifetime of your community. Using our account securing methods in place, such as Two Factor Authentication will help secure your account. We also have security items in place like brute force login protection, our firewall, and other security measures in place which should help aid in malicious attacks.

The best thing to do would be to setup Two Factor Authentication for all your administrators and moderators if you haven't already: