OTTAWA - The federal privacy watchdog says some leading Canadian websites are inappropriately leaking users' personal information to third-party sites such as advertising companies.

The information includes names, email addresses and postal codes -- apparently without consent and possibly in violation of federal privacy law.

Research commissioned by the privacy commissioner's office turned up significant concerns with about one-quarter of sites tested.

For instance, says the privacy watchdog, when people signed up online to receive promotions from a shopping site, their email address, username and city were disclosed to analytics and marketing firms.

Privacy commissioner Jennifer Stoddart says the websites -- which she has decided not to name publicly -- are sophisticated operations run by large organizations.

She has written to 11 organizations seeking information about their practices and, in some cases, explanations as to how they will make changes to ensure compliance with privacy law.