My WP was hacked & I can’t get rid of it

I discovered a couple of days ago that my WP had been hacked. I deleted the offending files – or so I thought – and re-installed the newest version of WP. However, there’s still a problem.

The host is godaddy (I’m not very familiar with godaddy – it was chosen by a neighborhood ass’n, a not-for-profit group, so there are a number of us working together.) After using FTP to delete the files I thought were a problem and that was insufficient, I used godaddy’s file manager to delete the rest. But apparently I didn’t rid the system of all of the evil files.

Does anyone have any suggestions as to how to fix this – it’s totally new to me. The files that were added in had na_ preceding each of the filenames if that helps narrow it down.

Furthermore, assuming I can rid the site of this, what do I need to do to prevent its recurrence? Thank you SO much for any help or guidance you might be able to offer.

Regards,
Penny