Within minutes of the bombing at the Boston Marathon, CNN put up a simple message on the front page of its website: "Are you there? Share images on CNN iReport."
Even though other news outlets pulled photos and videos from social media sites, CNN's strategy was by far the most effective use of what have become known as citizen journalism and crowdsourcing.
CNN received more than 400 files. One of the best came from an Emerson College student, Erin Farley, who was covering the race for a class. Clearly upset by the experience, Ms. Farley held her composure to file one of the most complete reports on what was happening just after the explosions. (Her work can bee seen at http://bit.ly/Zm13L4.)
CNN received dozens of photographs from a variety of angles, including overall shots from a building nearby, photos of the police and rescue workers in action and pictures of people expressing their sadness but also their hope for the days ahead. The iReport pages had tens of thousands of views.
One Instagram user drew a purple infinity sign on his hand and urged people to wear purple in support of those who had a loved one or friend injured or killed. Social media users started the hashtag, #purpleforboston, to spread the word.
Despite this excellent use of crowdsourcing and social media, such practices can prove dangerous.
The issue comes back as it often does in journalism to the basic tenets of reporting. Information needs to be verified as accurate. Two sources are always better than one, but that doesn't mean 200 tweets are better than two good sources. Twitter still provides a lot of bad information. For example, some of the falsehoods included a photo of a man who planned to propose to his girlfriend, but she reportedly was killed in the attack. (See more at http://bit.ly/17F7jkC.)
An editor needs to maintain quality control about what goes into a newspaper, what's on a radio or television broadcast, and what appears on a website. Alas, fewer editors exist, so inaccurate information circulating on social media makes it way onto websites.
During the shootings in the Newtown, Conn., school, for example, a variety of bad information got reported when it appeared on social media. The shooter was named incorrectly; the role of the shooter's mother at the school was wrongly characterized.
During the Arab Spring uprising, National Public Radio used crowdsourcing via social media superbly to get a bird's-eye view of Tahrir Square in Cairo from people in different locations around the huge plaza.
But crowdsourcing and social media failed to predict the eventual outcome of the Arab uprising an Islamist rather than a popular takeover of many Arab governments. The point here is that you still need journalists on the ground to dig deeper into what's being said on social media, which have a younger demographic than other media.
Social media tend to work well by providing images and information during a breaking-news event. Now comes the speculation of who planted the bombs in Boston and why. North Korea was the early leader, but the Twittersphere has turned toward the Islamic world. We should all wait until police authorities actually come up with the evidence and find those responsible. So I'll tune out of social media on this tragedy until then.
A personal note: One of my former students, Kurtis Lee, was a key reporter on The Denver Post team that won the Pulitzer Prize on the same day as the Boston Marathon attack for another tragedy: the movie theater massacre in Colorado.
• Christopher Harper is a professor at Temple University. He worked for more than 20 years at The Associated Press, Newsweek, ABC News and "20/20." He can be contacted at firstname.lastname@example.org.