Well, you really don't need the complete file either. Since torrents are usually shared unzipped, they can just replace a chunk with a bad one (It varies usuall

Well, you really don't need the complete file either. Since torrents are usually shared unzipped, they can just replace a chunk with a bad one (It varies usually from 256KB-2MB) and a single chunk can be replaced with a bad one embedded with malware to cause problems. Especially something like a buffer overflow attack on a video file.