Spam blog posts on Wordpress 3.4V

How do I fix this issue?

[Young_Bee]

Hi
Our wordpress blog is hacked recently where blog (not comments) is posted randomly on irreverent topics with authorized user name. It’s pretty old blog. We are using wordpress 3.4V & the theme is 1211. How do I fix this issue? Can the server update help us resolve this issue?
We regularly visit our blog page to find spam post & then delete them.

[bhukkel]

Unless it is shared hosting reinstall your OS, install all updates and the newest Wordpress version. Restore your data from a safe backup from before the hack.

[Young_Bee]

Sorry, not clear to me. Do you mean to say if it's a shared hosting, I should follow that process?
Just a heads up- we are using a dedicated server.

[bhukkel]

I meant to say when your site is hacked your complete OS is not trusted anymore. Hackers could have install a backdoor and updating Wordpress is in my opinion not enough. If possible reinstall your OS and restore a clean backup.

Enable autoupdate of Wordpress if the site is not critical.