Droppers are specially crafted PHP scripts which payload is to download (drop) a second malicious file and execute it. The dropped file can be a backdoor, hacktool, defacement or spam-seo related malware.
Any vulnerable website. Outdated software or compromised passwords can act as an infection vector.
Inspect your site's files looking for suspicious eval() entries or calls to third-party websites.. Also you can sign up with us and let our team help you restoring your sitea and removing any remaining malware for you.