FYI, this won't hurt your website from an SEO point of view. Unsolicited one way backlinks can never hurt you (if you purchase links those one way backlinks can hurt you). If they could then tactics like this would be an easy way to sabotage your competition. At worst, one way backlinks have no value. This is probably the case with the links you are referring to. The only way these links can harm you is if you link back to them. Once you do that you run the risk of being seen as part of a link scheme or link farm. That's when the penalties come into play.
If you're worried about your company's reputation I still wouldn't worry about it as the only people who actually check to see who is linking to your site is competitors and people doing SEO research (which is usually your competitors). Normal people don't check and almost certainly have no idea what a backlink is much less what a high or poor quality one is.
But to answer your specific questions, no, there is no way to discredit them or disavow them. You can't control who links to you or who sees those links. You can do as Ben recommended and contact the site administrators to let them know of their potential security problems and request the links be removed. But in practice that's probably not a good use of your time as the links aren't hurting you, and although unlikely but still possible, they may even be helping you if they have any value at all.
update 2102 -11
Google now allows you to disavow links