WordPress’ popularity makes it a frequent malware target. If you suspect your site has malware (and even if you don’t), you should scan it for free with Sucuri SiteCheck. The scan checks for several types of malicious threats. Here’s a screenshot of what you want to see; all green checkmarks.
If the scan finds malware and you don’t already know someone who can clean it up, you can pay Sucuri to do it. They have a good reputation and their pricing is reasonable. None of my sites have been infected yet, but if some day they are, I’d seriously consider using Sucuri.
Sucuri provides the free Sucuri Sitecheck Malware Scanner plugin for WordPress. Also, you should definitely watch the WordPress security webinar by Dre Armeda of Sucuri. Dre is one of the hosts of the WP Candy podcast WP Late Night, one of my favorite WordPress podcasts.