First, the responses saying that visitor browsers are giving warnings is that you're mixing http with https requests. That is a function of the browsers and is both common and correct.
Second, my host(s) have implemented a daily maldet scan which does scan for malware and can detect malicious code which may be placed on your site.
Third, once maldet is detecting no malware, then you can implement a hash validation of your files to report to you which files have been added, which have been deleted and which have been altered. As the webmaster, you can then compare those with your activities and investigate any anomalies.