They look like error/core dump files from the server. Nothing threads related. All your data is in the MySQL database, you won't be able to access any data via FTP. No threads files (with an exception of config.inc.php etc....) are modified or added within threads.
You should be able to dump them. If they continue to reappear, I'd ask your webhost about them.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.
