F-Secure Security Cloud API for AWS
campaigns.f-secure.com
campaigns.f-secure.com
Not sure why they're binding this to the AWS Marketplace. Safe Browsing is also free, though I'm not sure how comprehensive it is.
"5,760 checks/day"
If you use the Safe Browsing APIs (v4) to warn users about unsafe web resources, the following restrictions apply:
Lookup API (v4): You can query up to 500 URLs in a single POST request.
Lookup API (v4) and Update API (v4): A single API key can make requests for up to 10,000 clients per 24-hour period.