Many people report receiving notifications from their ISPs after downloading files using torrents. How will your ISP know? It’s all about how BitTorrent works. BitTorrent is much less anonymous than it might seem at first glance.
How do torrents work?
Downloading over the Internet involves receiving data from a remote server. Other than the initial request you send to get a file, most downloads are a one-way street. You get data from a central server and you don’t have to send anything from your server. Loading web pages, watching videos online, and downloading games on Steam all work this way.
However, if you download too many IP addresses from the same server at the same time, this can lead to clogging and slow download speeds.
Torrents are different from typical Internet downloads because they follow a peer-to-peer protocol. A swarming torrent is a group of IP addresses simultaneously downloading and uploading a file. Instead of just downloading a file from some server, you also download parts of it to other people. Because of this constant exchange process, the file associated with a torrent often downloads significantly faster than a standard download.
BitTorrent is often used for piracy. However, there are many legitimate ways to use a torrent. Because they can be paused, resumed, and split into smaller parts, they are ideal for downloading large files such as games, software, plugin packages, and updates. They are also a common method for distributing free music and videos.
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What does your ISP see?

Your ISP can’t immediately tell if you’re using BitTorrent, and can’t tell you what you’re downloading from it. Most torrent clients have some form of encryption that makes it hard for ISPs (and your home router) to identify this BitTorrent traffic. However, there are several ways to know that you are using BitTorrent to download something.
Downloading torrents exhibits some very obvious usage patterns such as multiple simultaneous download streams and many different TCP (Transmission Control Protocol) connections because you are talking to many IP addresses at the same time. If your ISP is actively trying to detect torrent usage, they will most likely be able to detect it.