Software is software. You’re downloading shady software off the Internet anyway, but there’s one key difference:
- Torrent sites (such as The Pirate Bay) usually have systems of trusted uploaders. These are marked with a green/purple skull next to the file in search results.
- A torrent with a large number of seeders (think: hundreds or thousands) is less likely to contain a virus because nobody honest would seed a malware torrent and it’d cost a lot to fake that many seeders across the world.
- Torrenting software verifies the integrity of downloaded data. It uses a cryptographic hash function for this so it’s impossible for a seeder to send you a tampered file (that is different from the file you intended to download). When you use a torrent file or magnet link, it contains the hash of the file so if what you receive does not match the hash then the torrenting software will discard it.
A “couple hundred peers” is a lot easier said than done. That being said, it does happen and you are correct that having a lot of seeders doesn’t guarantee a safe download.
All of the three conditions I mentioned are neither sufficient nor necessary for a safe download, but there is a strong correlation. Unless the torrent is official (e.g. official Linux distro torrents), there is always some chance of a bad download. The chance can be low but is never zero.