David Johnson worried that his e-mail software client was in trouble when rumors started cropping up online.

Criticism is one thing, says Johnson, CEO of Atlanta-based PR firm Strategic Vision. But in this instance, people were posting online messages warning not to use his client's product "or their entire system would shut down."

That's quite an admonition. So Johnson took the offensive to combat the potential brand-damaging misinformation.

"We treated it as a joke," he recalls. His firm addressed the comments in a ...