A /. article pointed me to the blog post Reporting Vulnerabilities is for the Brave. Sounds familiar. Been there, done that. A customer had a Web site, and I told them about a problem. They told their vendor. And the vendor went after me - probably because, like most security-unconscious companies they felt threatened in one way or another.
Therefore I wholeheartedly agree with the instructions outlined, plus: lean back, and enjoy when the bad guys whack that company. Yes, this is controversial, but as long as companies don't "get it" that there are people that want to help them when reporting vulnerabilities, it is definitely better to keep your trap shut.
Aside from the cynical advice in the above paragraph, here is something to consider for your company: establish a policy - and publish it! - that you welcome security reports by security researchers (and Joe Average for that matter). This goes a long way to getting the threats mitigated before they are exploited.