Mr. Wales and Mr. O’Reilly were inspired to act after a firestorm erupted late last month in the insular community of dedicated technology bloggers. In an online shouting match that was widely reported, Kathy Sierra, a high-tech book author from Boulder County, Colo., and a friend of Mr. O’Reilly, reported getting death threats that stemmed in part from a dispute over whether it was acceptable to delete the impolitic comments left by visitors to someone’s personal Web site.

Distraught over the threats and manipulated photos of her that were posted on other critical sites — including one that depicted her head next to a noose — Ms. Sierra canceled a speaking appearance at a trade show and asked the local police for help in finding the source of the threats. She also said that she was considering giving up blogging altogether.

In an interview, she dismissed the argument that cyberbullying is so common that she should overlook it. “I can’t believe how many people are saying to me, ‘Get a life, this is the Internet,’ ” she said. “If that’s the case, how will we ever recognize a real threat?”

Ms. Sierra said she supported the new efforts to improve civility on the Web. The police investigation into her case is pending.

Menacing behavior is certainly not unique to the Internet. But since the Web offers the option of anonymity with no accountability, online conversations are often more prone to decay into ugliness than those in other media.

Nowadays, those conversations often take place on blogs. At last count, there were 70 million of them, with more than 1.4 million entries being added daily, according to Technorati, a blog-indexing company. For the last decade, these Web journals have offered writers a way to amplify their voices and engage with friends and readers.

But the same factors that make those unfiltered conversations so compelling, and impossible to replicate in the offline world, also allow them to spin out of control.