This NY Times article provides a useful primer on crisis communications.  See In Case of Emergency: What Not to Do. A few excerpts follow:

Whoever suggested that all publicity is good publicity clearly never envisioned the wave of catastrophe engulfing high-profile corporations over the last year, laying waste to some of the most meticulously tailored reputations on earth.

The calamities have served up a lifetime supply of case studies to be mined for lessons on best practices, as well as pitfalls to avoid when disaster arrives.

As conventional wisdom has it, the three companies at the center of these fiascos worsened their problems by failing to heed established protocol: When the story is bad, disclose it immediately — awful parts included — lest you be forced to backtrack and slide into the death spiral of lost credibility.