Internet speed tests have shown that Time Warner Cable has repeatedly failed to provide the speeds it promises customers, according to a New York state government official. New York has not publicly released any data to back up the claim, but apparently shared the results with the cable company. Charter—TWC's new owner—received a letter demanding improvement yesterday from the New York attorney general's office.

"We recently called on New York customers of major broadband providers to use open-source tools to test the Internet speeds they were experiencing," NY Senior Enforcement Counsel Tim Wu wrote to Charter CEO Tom Rutledge. "The results we received from Time Warner Cable customers were abysmal. Not only did Time Warner Cable fail to achieve the speeds its customers were promised and paid for (which Time Warner Cable blamed on the testing method), it generally performed worse in this regard than other New York broadband providers."

The Washington Post published the full letter and has a related article.

Wu—coiner of the phrase "network neutrality"—has been investigating the speeds delivered by TWC, Verizon, and Cablevision. Wu's letter did not include specific numbers, saying the results are "preliminary," but "troubling." Wu declined to make the numbers public when contacted by Ars.

Wu's letter castigated TWC for promising "blazing-fast" and "super-reliable" Internet connections in advertisements, while providing substandard service. Wu wrote:

[I]t appears that the company has been failing to take adequate or necessary steps to keep pace with the demand of Time Warner Cable customers—at times letting connections with key Internet content providers become so congested that large volumes of Internet data were regularly lost or discarded. This translates into degraded performance for customers, including those using popular on-demand video services, like Netflix—despite specific promises from Time Warner Cable that they could stream video content reliably and with “no buffering.” The problems appear to have been particularly acute at primetime, precisely when many customers log on or tune in. Customers have been frustrated, as movies freeze, websites load endlessly, and games become non-responsive. In addition, it appears that Time Warner Cable has been advertising its Wi-Fi in ways that defy the technology’s technical capabilities and has been provisioning some of its customers with equipment that simply cannot achieve the higher bandwidths the company has sold to them.

Wu told Rutledge that he'd be in touch soon to "propose next steps."

Federal Communications Commission testing in customers' homes previously found that some TWC customers aren't receiving the speeds they pay for. The FCC's Measuring Broadband America report found that about 10 percent of TWC customers got less than 80 percent of the advertised download speed during peak usage periods. About 15 percent got between 80 and 95 percent of advertised speeds, and about 75 percent got more than 95 percent of advertised speeds.

Charter indicated it will make improvements in the networks of Time Warner Cable and Bright House, another cable company it just acquired.

"Charter has made significant investments in our core infrastructure which has enabled us to offer high-value products backed by a high-quality service organization throughout our footprint," Charter said in a statement published by the Post. "As we progress with the integration of Time Warner Cable and Bright House Networks, we will continue to do the same."

We've contacted Charter and will provide an update if we get one.

Disclosure: The Advance/Newhouse Partnership, which owns about 13 percent of Charter, is part of Advance Publications. Advance Publications owns Condé Nast, which owns Ars Technica.