core.**** Files

Hi
A whole bunch of files named core.10984, core.11784 etc have suddenly appeared in the root directory of one of my WordPress blogs.

Are they legitimate, or has my blog been infected with a virus?

I believe I have pretty good security in place with WP Firewall2, Login Lockdown, and Paranoid911, and I always do a manual install.

Some info on these files would be apprecialted.

Thanks
Anne