What you need to do:
1) First of all, make sure you are using the latest version of WP core, Themes as well as Plugins.
2) Secondly, check the scripts for any unauthorized modifications or unknown scripts injected in the webfiles.
3) Thirdly, change all your hosting passwords to a more complicated passwords (consists of symbols, alphanumeric characters, lower and upper case letters). E.g FTP login, Control Panel hosting login and as well as your CMS login password.
4) Scan your local computers with a well-known anti-virus software and install Microsoft Security Essential for those users’ Computers that use Windows platform.
5) Check and find the root cause by disabling the WP’s plugins that usually cause high CPU usage and check with us.
6) Consider installing this WP Plugin –> “WP Super Cache” for those websites using html pages. —> A very fast caching engine for WordPress that produces static html files.
7) Alternatively, try out another useful plugin –> “DB Cache Reloaded”. —>This plugin caches every database query within given lifetime. It is much faster than other html caching plugins and uses less disk space for caching.
Follow the steps below:
1) Check thoroughly the index.php scripts (check if there are any abnormal or injection scripts) inside this file.
2) Check and disable all your WP plugins and enable one by one to pinpoint which Plugin is causing the overload.
3) Change all your hosting (e.g FTP, WP login, or Control panel) login passwords to more complicated passwords.
4) Patch all your hosting webfiles, 3rd party apps, plugins and themes to the latest version.
5) Scan your local computer which you use to connect to the hosting with a well-known anti-virus. If you are using Windows platform – install Microsoft Security Essentials.