There is a thread in the User Assistance forum (I think). It relates to Sixty-Fiver's own website which was hacked recently. However, according to the response from Tom Stormcrowe on that thread, Sixty-Fiver has fixed the problem, but google's malware warning system still has it listed.
Personally, I think that if you are going to post a picture, do it as a jpeg attachment rather than a link. That way, it remains permanently accessible to this site's users, rather than hundreds or thousands of empty boxes appearing on threads like the Century Bicycles one because the linked sites have expired, or the photos have been removed by the user without thinking of the links to it. And it avoids these malware notification issues.