There is no one foolproof method for securing your WordPress installation against attacks.  You simply follow a series of best practices against known attacks.  Some new hack can always come along tomorrow and make you vulnerable.  You do what you can and hope for the best.  The following is a quick guide to some precautions.  Any of the details can be easily Googled or found here wp-security-scan if what I wrote sounds like a foreign language.

The easy way out: 

• First thing is to upgrade to the latest version of WordPress, 2.5 as of this writing. 
• The following two plugins are of some help.  Bad Behavior will repel most spambots. 
• WP Security Scan will analyze your installation to see what securty loopholes you have in your system.  Most of the advice that follows is covered by this plugin as well.

Common Sense: 

• Never use your public email address or your WordPress Author name for any of your secure logins. 
• Make separate emails for each account and track them using Roboform. 
• Make your passwords long and alpha-numeric. 
• Don’t use your real contact details for your domain hosting registration. 
• Don’t give out your passwords for any reason.

The nitty gritty:

• Add a blank index.html to your plugin directory so it can’t be opened. 
• Add a .htaccess file blocking your wp-admin directory from anyone but your home computer. 
• Make your public_html directory non-writable. 

Advanced stuff: 

• Change the “wp_” prefix in your sql tables to something else.  The WP Security Scan plugin will do that for you.  Note-this is a major pain if you have a huge database of 1000’s of posts.
• Block anonymous tor access by using the latest list of exit nodes and IP block them. 

Even Then:  You can’t be certain there isn’t some undiscovered loophole.  So make backups on a regular basis and download them.  If someone does hack your account, contact your Hosting company.  They will help you restore from backup.  then change all your passwords that may have been compromised.  Examine your homepage for any sign of hidden links that have been added to your header or footer.  To do this in Firefox, go to tools/pageinfo/links and look for anything suspicious.