This collection of useful links on the Google Developers’ Blog is well worth a look. It gives you an idea of what you’re up to if somebody chose to use your site as a malware delivery channel:
Our new Help for hacked sites series includes articles and 80+ minutes of video to help you, and to help you help others. In the overview video, these common questions are addressed:
Why would someone ever want to hack my site? (often asked by our trusting friends 🙂 )
How was someone able to hack my site?
What’s the process for fixing it and how long will it take?