Live blogging service CoveritLive conceded late Friday that "proprietary data files" had been accessed by unknown users.
The firm said the hack started about January 7 this year.
It said the extent of the hack was "not yet determined" but that "no financial account information has been compromised".
The company said it was enforcing password resets for all users, although it also said there was "no evidence" that the hacker had retrieved any such data.
