Sucuri SiteCheck is an online scanner that allows detect malicious elements on a website, ideal to carry out a primary analysis in case of infections. The service is free and offered by the company Happened which is dedicated to monitoring and removing malware.
The following are some examples of analysis and detections, something very good about the tool is that it indicates quite accurately where the malware or malicious item is located, in addition to providing some details about the problem.
Example of a website currently infected with a hidden iframe:
And the details of the detected malicious element:
Another example, a educational site with pharmaceutical spam:
More spam but in a government site:
Blog with WordPress outdated and infected with malicious scripts:
I hope the information is useful, I discovered the tool thanks to the official forum for Google Webmasters where several users dedicate part of their time every day to share knowledge and help others.
See also: More tools to analyze and detect dangerous sites.