There is a huge vulnerability (zero day) that could allow hackers to upload and execute malicious code. Many themes/plugins use it (estimates are hundreds of thousands) so check to see if your wordpress themes/plugins have timthumb.php (or do a cpanel search for it) and either clear the file and save or update it (although I hear the "fix" released might still be vulnerable so that would be at your risk).
Sometimes the theme developer calls it thumb.php rather than the full name, so be on the lookout for those as well.