The best way to check your website for any malicious content such as viruses and backdoors is to download yourpublic_html folder to your local computer and run an antivirus scan on it.
You can download your public_html folder using your favorite FTP client.
For the antivirus scan use reliable updated antivirus software such as Norton Internet Security or Kaspersky Internet Security. They can detect almost all viruses and exploits.
Once your public_html folder is cleaned, you can remove your old public_html folder from your account and upload the cleaned one.
For more information on how to keep your account secure, please check our basic security guidelines.