WordPress just released another update since a major one last month (ver 2.5). The new version 2.5.1, includes over seventy bug fixes including security fixes. Check out the full list of fixes made in 2.5.1 here.
As for added security, all is advised to place a secret key in their wp-config.php file. If you can’t come up with your own secret key, you can let WordPress generate a random secret key for you by clicking the “visit this link we set up to get a unique secret key” in their blog post. Just copy the entire line of code and paste it into your wp-config.php file (or overwrite this line if it exists: define(‘SECRET_KEY’, ‘put your unique phrase here’); // Change this to a unique phrase).
Reminder: To update, just copy everything to your host EXCEPT the wp-content folder. Copying the wp-content folder to your server will delete (overwrite) your currently installed themes and plugins. Always remember to backup.