If you are a member of a decent private torrent site then you can easily get old stuff as it will be cataloged in to a pack. For example shows that have finished will have complete seasons pack. Shows that are currently running will have packs by seasons. Movies will have packs by actor, genre or series. These are usually seeded by at least 1 person with a seedbox. Some sites coordinate seeding them.
Viruses on private torrent sites are rare as you can report torrents to staff to be removed. Most torrents are scene anyway. Older stuff is just usually repacked scene stuff.