I don't infer the same from the quote. It just as easily could have been her single source, Mitnick, that are the 'hacker circles'. The wording alone does not suggest multiple sources.
It's background info confirmed by at least one and probably multiple sources, and journalists specifically don't want to or need to footnote their stories with multiple named sources like a research paper or legal brief.
If it's not shoddy journalism, then it's shoddy writing.