You may occasionally see on Google a notice that says “This site may harm your computer.” We place this warning in search result snippets when we see signals that a particular web page may be spreading malware. Webmasters occasionally will see this warning on one of their pages that wasn’t intended to be malicious. This is because sometimes your site could be distributing malware — and you might not even know it or be able to easily find it. Malware details https://googlewebmastercentral.blogspot.com/2009/10/fetch-as-googlebot-and-malware-details.html is designed to help webmasters track down what on their site is triggering this label and clear the problem — thus, making their page (and the web) safer for users.
Source:
https://googleblog.blogspot.com