know it so can someone else. (Brute force attack or man in the middle) Denial of Service attack (DDoS) flood your site with more traffic than it can handle Through a theme, file or plugin Through your FTP or CPanel. (Files set to read, write,execute. Brute force, anonymous login, shared hosting infection) @michele_butcher
when they have completed their job. If they have posts on your site, you can knock them down to subscribers so they can not change anything on your site. If they are only doing work, delete them when their job is done.
plugin. Two versions a free and a premium. http://ithemes.com/security @michele_butcher Brute Protect If you are mainly worried about DDoS attacks, Brute Protect has you covered. http://bruteprotect.com
they are changing in your site. iThemes Security and other security plugins give you the option to see what all users are doing when logged into the dashboard.
content, update everything and update often! The biggest source of nearly all hacks as once something is patched, it is trivial to get into the old stuff. @michele_butcher
envato (Themeforest, code canyon) always check the box to be notified of updates. they will not tell you otherwise This is why the RevSlider SoakSoak infection was so widespread. Many didn't know the plugin was built within the theme.
the plugins you are using at that time on your site. You can always upload them again later. Only have your theme you are using on your site. If something is not active, delete it. @michele_butcher