What is secureserver net? Why did it access my gmail account?

Godaddy-hosted email (if you choose to host your email through godaddy) is hosted under the "secureserver net" domain. In fact, the addresses you configure into your mail client are pop.secureserver.net, imap.secureserver.net, smtp.secureserver.net, etc. If you configured your Godaddy webmail (for perhaps some other domain) to pull in mail from your Gmail account, then you will see it show up as going to secureserver.net rather than whatever domain your mail is registered under. And if you didn't do it, someone else did. Hackers frequently go through intermediary services to mask their identity. This is as likely an answer as any. So... change your password