AN article in PC Magazine last week revealed that customers across the country have received letters from Comcast warning them to limit their bandwidth consumption or face a one-year termination of service.

The company, though, “is refusing to reveal how much bandwidth use is allowed, making it impossible for customers to know if they are in danger of violating Comcast’s limit,” according to the article’s writer, Chloe Albanesius.

Ms. Albanesius also spoke with customers who said they had already paid the ultimate penalty.

Frank Carreiro, a resident of Utah, had his service cut off in January, and has been blogging about it at comcastissue.blogspot.com. He started the blog in part because “silence will only encourage the company to continue abusing its customers.”

Comcast’s network security department warned Mr. Carreiro in December to reduce his use of bandwidth. He called customer service several times, he said, and was told that there was no record of such a warning and that he might have been the victim of a prank call. A month later, he said, his service was disconnected. He has since switched to D.S.L. service and is “very happy.”