Sorry for the delay in replying, had to go out of town after I posted originally. Here is the extended information provided by Yandex, but the more I look into it, the more I think it is a false positive.
Yandex periodically checks websites to warn users about harmful webpages. The last check (less than a week ago) showed that this site contains malware. This can happen either in accordance with the owner's intent or due to the tampering of fraudsters.
How Yandex verifies sites
Here is a good page with details regarding Mal/Iframe-W from Sophos, hopefully it helps pinpoint the possible source if you haven't already.