I have been invited but I never invited the user, how is this possible?

[컴퓨터공학부_이정은]

I received an email today at 9:17 a.m. that a user was invited, but I wasn't using Jira at that time because I was doing something else. I've never used Jira before, and the user who was invited deleted one of the project items at 9:20 a.m. Other team members also confirmed that they weren't using Jira at that time. I've never heard of this person before and I don't know how they were invited.

[Brant Schroeder]

@컴퓨터공학부_이정은 Welcome to the Atlassian community

I will escalate to Atlassian so they can look into this more.  I am assuming that one of your administrator accounts has been compromised.  I would suggest having your administrators change their passwords and enable two factor authentication - https://support.atlassian.com/atlassian-account/docs/manage-two-step-verification-for-your-atlassian-account/   This will help prevent against compromised accounts.  If a user has a computer with a virus or they are using passwords that have been skimmed off of an account with a matching password this is how the account would become compromised.  Using a unique password for Atlassian and two factor authentication will minimize risk.