(New York Times) — It might just be the most worrisome letter to the editor any news organization can receive. PBS fought on Monday and Tuesday to restore the Web sites for two news programs on public television, “Frontline” and “PBS NewsHour,” which were crippled by hackers who said they were angered by coverage of WikiLeaks. The incidents were the latest examples of what security experts call “reputational attacks” on media companies that publish material that the hackers disagree with. Such companies are particularly vulnerable to such attacks because many of them depend on online advertising and subscription revenue from Web sites that can be upended by the clicks of a hacker’s keyboard — and because unlike other targets, like government entities and defense contractors, they are less likely to have state-of-the-art security to thwart attacks. The PBS attack was said to be motivated by a “Frontline” film about WikiLeaks that was broadcast and published online on May 24. Some supporters of Julian Assange, the WikiLeaks founder, and Bradley Manning, a soldier who is suspected of having shared hundreds of thousands of government files with WikiLeaks, criticized the film and claimed that it portrayed the two men in a negative light.