I have reset my PC and changed my passwords. As long as the user has logged out, there shouldn't be anymore issues. I'll still leave it in my signature to not do any trades with them for a couple more days.

I have signed a message from my Bitcoin address I have been using for years:

Address: 1GhxHtabWhEpdb7e7oEJ2vd542n33BwTHR
Signature: IF0ceAT043WeE9+pTH0ZhAG8WOPmbe9gp+/2aQk9bwY6f723M0m54cbSgUym/3qR8gU2WNgwHJADa9TSj85Iui0=

You can verify that address has been in use for many years by searching through my posts. Thank you guys!