The Center for American Progress writes to say that its staffers fully identified themselves in their communications with Kim Eisler over the Abramoff e-mails. From Judd Legum of CAP:

I can tell you definitely we did not misrepresent ourselves to Eisler. Our very first e-mail to him identified us as from the Center for American Progress, a non-profit. All of our e-mails to him were from our americanprogress.org e-mail accounts and contained links to the Progress Report and ThinkProgress.
Even though there was no talk of our communications being off the record, we took the additional precaution of asking him if we could publish what we learned from him on our blog. He said we could and that we could use his name.
In short, we were completely transparent in all of our communications with him.