The Max Planck Institute for Software Systems  released a study Thursday showing that Cox Communications and Comcast have been blocking BitTorrent transfers within the United States at both peak and non-peak hours.

Overall, the study focuses on whether BitTorrent upload traffic has been manipulated at 8,175 different locations around the world by using a testing suite called Glastnost. While only around 7.7% of hosts worldwide reported having their BitTorrent traffic throttled, 87.8% of all blocked hosts were located within the United States, where nearly one-quarter of all hosts tested experienced blocked BitTorrent traffic. Of those nearly 600 blocked hosts, the vast majority were located on Comcast or Cox networks, the study reports. What's more, says the study, all blocked hosts in the United States are located on cable networks.

The study also finds that both Comcast and Cox block BitTorrent uploads during both peak hours and during mornings and weekends, when traffic is typically less heavy. Comcast, for instance, blocked BitTorrent traffic on just over 60% of all tests conducted on Saturdays, which is a slightly higher percentage of tests blocked during weekdays; on Sundays, the percentage of blocked tests drops significantly to just over 50%. Cox, on the other hand, was more likely to block BitTorrent traffic on the weekends than on the weekdays, with nearly 70% of all tests conducted on Saturdays and Sundays blocked. The institute qualifies the Cox data, however, by noting that Cox tests comprised a much smaller sample size than the Comcast tests.

The institute says that all tests for the study were conducted between March 18 and May 15. Comcast said back in March that it had agreed to stop targeting BitTorrent uploads or any specific individual protocols in its traffic-shaping practices. Although the company did not set a specific date for when it would stop targeting BitTorrent, it did say that it hoped to have its new traffic-shaping protocols in place by the middle of the year.

In a statement issued Thursday, Comcast took issue with the institute's assertion that it was blocking traffic and said that a more accurate term for its practices would be traffic management.

"Comcast does not, has not, and will not block any Web sites or online applications, including peer-to-peer services like BitTorrent," the company said. "We have acknowledged that we manage peer-to-peer traffic in a limited manner to minimize network congestion. While we believe our current network management approach was a reasonable choice, we are now working with a variety of companies including BitTorrent."

Comcast has been under fire from such advocacy groups as the Electronic Frontier Foundation and Free Press since last October, when the Associated Press reported that the company was actively interfering with some of its customers' ability to share files online.

Essentially, the AP has reported, Comcast has been employing technology that is activated when a user attempts to share a complete file with another user through such P2P technologies as BitTorrent and Gnutella. As the user is uploading the file, Comcast sends a message to both the uploader and the downloader telling them there has been an error within the network and that a new connection must be established. Because the message sent to users does not appear to be sent directly from Comcast, many critics have accused Comcast of sending forged or spoofed packets that they say are deceiving to consumers.