A pillar of the American media establishment took a knock on Wednesday with an admission of plagiarism in a video essay attributed to CBS anchor Katie Couric.

Couric's producer was sacked and her network obliged to apologize for the incident which occurred in a commentary called Katie's Notebook, which purported to be a personal essay from the anchor and was posted on her blog.

Couric, who became the first woman to serve as the solo anchor for the evening news on one of the traditional big three networks, was horrified to learn of the plagiarism, said press reports.