This isn't to say that outside issues (such as someone raising a complaint) aren't worth your attention. In fact, if it looks like an unhappy customer or ex-employee has posted damaging information (whether true or false), it is just as important to handle that quickly and effectively.
Second step: Action (and apology)
So now that you know something needs to be done, what do you do?
First, you have to publicly acknowledge that there's an issue. Don't try to come up with a perfect answer at first; a speedy reply that indicates you've heard and understood is better than a detailed one that's a week late.
Create a space for the reply that is easy to get to and easy to pass around and that has at least some degree of permanence. A blog post is the best default choice, but make sure the post is on a blog that is clearly an official mouthpiece for your organization. Don't create a blog just for the reply.
If the explosion was on Twitter itself, use Twitter to draw attention to your follow-up, but don't use Twitter to issue the apology or clarification. Let's face it -- 140 characters are not enough for something so nuanced, even if it's just your initial reply.
After your first acknowledgement, take time (not too much, though) to craft a more detailed response. It doesn't have to be exponentially longer than your original note, but it should contain three things:
1. Your understanding and acknowledgment of the problem.
2. Affirmation that you have learned from the situation.
3. The steps you're taking to correct it now and prevent it from happening in the future.
Nivea did something interesting with social media as a way to address a gaffe that occurred in conventional media. When its "Uncivilized" print ad campaign that ran in the September 2011 issue of Esquire drew ire for being racially insensitive, Nivea publicly apologized, withdrew the campaign and created a page on its official Facebook site to call attention to the company's response, which read in part, "The advertisement offended many and for this we are deeply sorry. After realizing this, we acted immediately to remove the advertisement from all marketing activities."
The page was retired not long after the campaign itself receded from public notice. That serves as one example of how the longevity of the medium you use for your apology also matters. Social media can be ephemeral -- in other words, if the controversy has completely died down or become seriously outdated and if you don't need the public-facing response to be archived perpetually, you can remove it.
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