How BitTorrent Changed File Sharing and Why It Still Puts Your IP at Risk

BitTorrent (BT) is a peer‑to‑peer (P2P) file‑transfer protocol that many people know as a popular way to download large files such as movies, but it has also become a major channel for worldwide piracy.

On July 2 last year the protocol celebrated its 20th birthday; its creator, American programmer Bram Cohen, likely never imagined that this seemingly modest tool would shape the Internet ecosystem for decades.

Traditional download methods like HTTP, FTP, or POP use the TCP/IP protocol: a file is placed on a server and then the server sends the entire file to each requesting client, putting heavy load on the server. The diagram below shows this classic model.

BitTorrent works differently. It employs an efficient software distribution system and P2P technology to share large files (e.g., a movie or TV program). Each user not only downloads but also uploads parts of the file, effectively becoming a node that redistributes data.

For example, when users A, B, C, and D download the same file, BitTorrent does not pull the whole file from the original server for each user. Instead, it selectively downloads already‑completed pieces from other peers: if A has piece 1 and B has piece 2, C can obtain piece 1 from A and piece 2 from B, while A and B can simultaneously download missing pieces from C. The following diagram illustrates this process.

Thus, BitTorrent lets users distribute resources directly to each other; downloaders are also providers. This dramatically reduces the server’s burden, allows a single server to handle many large‑file requests without consuming massive bandwidth, and generally speeds up each user’s download.

In theory, the more popular a resource, the more participants share it, the greater the combined bandwidth, and the faster the download.

To help users locate resources quickly, Bram Cohen also designed BT “seeds,” which are small files that contain metadata about the shared content.

While the decentralized nature of BitTorrent made it popular, it also earned a reputation for facilitating piracy, leading to legal actions. One major issue is that BitTorrent easily exposes users’ IP addresses, making them vulnerable to subpoenas.

Recent media reports show that studios for popular movies such as “The Expendables 3,” “The Disciple,” and “After” compiled a list of 63 IP addresses and filed DMCA subpoenas with a Hawaiian court to obtain user information from ISPs.

With a subpoena, plaintiffs can compel ISPs to reveal the subscriber behind an IP address and pursue compensation. Because IP addresses are publicly broadcast in BitTorrent traffic, tracing infringers is relatively straightforward.

In one U.S. case, a man named Paul H was sued for downloading 145 pirated videos via BT seeds and was ordered to pay $108,750 (about ¥700,000). The court based the damages on the statutory minimum of $750 per work.

Chinese copyright law (Article 48) states that copying, distributing, performing, broadcasting, or transmitting works without the right holder’s permission constitutes infringement, regardless of profit motive. However, whether the infringer profited can affect the amount of compensation.

Domestic enforcement against piracy has intensified, but it still lags behind foreign jurisdictions where copyright protection is stricter and lawsuits are frequent.

In 2019, the operator of the “BT Paradise” site was sentenced to three years in prison and fined ¥800,000 for running a profit‑driven platform that offered magnet links and torrent files without permission.

Overall, while the “free lunch” of BT piracy is shrinking as legal risks rise, a gray‑area still exists where unauthorized sharing can persist.