They published this today:
The U.K. newspaper, which had alleged that Whisper violated users' privacy, added a paragraphs-long clarification at the top of a main article in the series. It also added a link to the clarification to other articles in the series, and removed a commentary from its website.
The Guardian's clarification blunted its earlier reports, which had raised broader questions about so-called anonymous messaging apps that promise users the ability to post without revealing their identity. The reports had also highlighted issues surrounding how publishers of such apps handle sensitive data, and the degree to which they compromise user privacy to obtain publicity.
The Guardian maintained that it didn't report that Whisper's activities were unlawful, and that the company still contests other aspects of its reporting. "The Guardian has clarified an article about Whisper's terms of service and removed an opinion article," a spokesperson said. "The substance of our original reporting remains unchanged."