Typically what happens is someone finds a way to get into your website and upload something. I don't see that you logged in when this happened, so I would guess that someone found a way to hack in. There's also a login from a blacklisted country in the last few months that was caught.
Additionally, your account hasn't been logged into since mid-December, so ultimately the account was suspended for not logging in for more than 30 days.
I will talk to the abuse team about the malicious software and see if the account is able to be recovered or if it's all in quarantine.