Comcast Is Secretly Throttling Your BitTorrent Downloads

Comcast has some explaining to do.

An Associated Press investigation published last month confirmed what BitTorrent users have suspected for months: Comcast is actively interfering with peer-to-peer file-sharing traffic on its network. The company isn't just slowing down BitTorrent — it's forging network packets to disrupt transfers altogether.

Here's what's happening, why it matters, and why the FCC is now getting involved.

What Comcast Is Actually Doing

The AP ran tests using a computer on Comcast's network in several markets. When they attempted to share files using BitTorrent, Comcast's network sent forged RST (reset) packets — essentially fake disconnect messages — to both the Comcast subscriber and the remote peer. The connection drops. The transfer fails.

This isn't garden-variety network congestion. Comcast's equipment is actively inspecting your traffic, identifying BitTorrent transfers, and injecting fake data into the connection to kill it. That's a deliberate, targeted interference with a specific type of internet traffic.

The technique is called deep packet inspection combined with RST injection, and it's particularly sneaky because the forged packets look like they're coming from the other end of the connection. As a user, your BitTorrent client simply thinks the remote peer disconnected. You wouldn't know Comcast was responsible unless you captured and analyzed network traffic at the packet level — which is exactly what the AP and several independent researchers did.

Comcast's Response: Deflect and Deny

Comcast initially denied the reports. When confronted with the AP's test results, the company shifted to vague corporate language about "managing its network to provide the best possible experience for all customers." They haven't disputed the specific technical findings.

The company argues that BitTorrent and other peer-to-peer applications consume a disproportionate share of network capacity, and that managing this traffic is necessary to maintain service quality for all subscribers. There's a kernel of truth here — P2P traffic does use significant bandwidth, especially upstream capacity. But there's a world of difference between managing congestion transparently and secretly forging packets to block specific applications.

If Comcast genuinely needed to manage congestion, there are legitimate approaches: rate-limiting heavy users during peak hours, investing in more upstream capacity, or implementing transparent quality-of-service policies. Instead, the company chose the most deceptive approach available — one that makes it look like the problem is with BitTorrent or the remote peer rather than with Comcast's own network management.

Why This Matters Beyond BitTorrent

Let's get something out of the way: yes, BitTorrent is used to pirate movies and music. It's also used for plenty of legitimate purposes — distributing Linux installations, sharing public domain content, and increasingly as a content delivery mechanism for legitimate companies. Blizzard Entertainment uses BitTorrent to distribute World of Warcraft updates to millions of players.

But the piracy question is a distraction from the real issue. This is about whether your internet provider gets to decide which applications you can use and which ones don't work properly on your connection.

Today it's BitTorrent. Tomorrow it could be a VoIP service that competes with Comcast's phone offering. Or a streaming video service that competes with Comcast's cable TV business. Or any application that Comcast decides uses too much bandwidth or threatens its other revenue streams.

This is the net neutrality debate made concrete. It's no longer theoretical. A major ISP — the largest cable broadband provider in America, serving around 13 million internet subscribers — is actively discriminating against a specific type of traffic on its network. And it tried to hide it.

The FCC Gets Involved

FCC commissioners have started asking questions. Commissioner Michael Copps called the reports "deeply disturbing" and said the Commission should investigate. Free Press and other advocacy groups have filed formal complaints with the FCC.

The question is whether the FCC will actually do anything. The Commission has adopted a set of internet policy principles that include the right of consumers to "access the lawful Internet content of their choice" and to "run applications and use services of their choice." Comcast's BitTorrent throttling appears to violate both principles.

But those principles are non-binding. The FCC hasn't adopted enforceable net neutrality rules, and under the current classification of broadband as an "information service," the Commission's authority to act is uncertain.

If the FCC does take action, it would be the first real enforcement of net neutrality principles against a major ISP. That would set an important precedent. If the FCC does nothing, it sends a clear signal that ISPs can discriminate against whatever traffic they want as long as they can claim "network management."

What You Can Do

If you're a Comcast subscriber experiencing BitTorrent throttling, your options are limited but not nonexistent:

Encryption. Many BitTorrent clients support protocol encryption, which makes it harder for Comcast's deep packet inspection to identify BitTorrent traffic. It's not foolproof — Comcast can potentially throttle all encrypted traffic — but it helps.

VPN. A virtual private network tunnels all your traffic through an encrypted connection, making it invisible to Comcast's inspection equipment. VPN services typically cost $5-10 per month and will slow your connection somewhat, but they prevent your ISP from seeing what applications you're using.

Switch providers. If you have DSL or another broadband option in your area, consider it. Not all ISPs throttle BitTorrent. This is the market solution — vote with your wallet. Of course, many Americans only have one or two broadband choices, which is exactly why this is a regulatory issue and not just a customer service one.

File a complaint. The FCC accepts consumer complaints online. Free Press has set up a page specifically for Comcast subscribers to report throttling. The more complaints on file, the harder it is for the FCC to ignore the issue.

The Precedent Being Set

What happens next with Comcast and BitTorrent will shape the future of internet freedom in the United States. If a major ISP can secretly interfere with lawful internet traffic and face no consequences, every other ISP will take note.

We're watching the net neutrality debate move from think tanks and policy papers into the real world. And right now, the real world looks a lot like Comcast deciding what your internet connection is for.