It's not just Bittorrent that is unsafe, it's basically the use of Torrents or P2P networks that is unsafe.
The reason behind this is cause the majority of files found on these networks tend to have a payload of Malware whether it be in the form of a simple worm designed to install a backdoor, then start downloading more parasitic content or a full blown Malware package such as can be found in some disk images.
There are video and audio files out there pretending to be what they are not, but when you go to play them, they ask you to install a needed Codec (fake of course) or some may actually play while at the same time they'll be installing a Malware package in the background. Then there are the ones which when you go to play them, they say you need to de-compress them first and that you must use a certain decompressor tool (fake of course).
So basically using such networks is much like a game of Dodge Ball. You need to be very careful and you need to check everything thoroughly.
While torrents and P2P might be a great way to get a hold of legitimate files from legitimate sources or even for exchanging files from trusted sources, it's all the other stuff and sources which are out there that makes these networks so unsafe.
The better way to get a hold of what you want would be through UseNet NewsGroups using a Primary News Server and a download client such as NewsBin Pro
For a Premium news server, I would recommend
EasyNews.com and they do have a 14 day Free trial
The
NewsBin Forums has a lot of useful information for beginners and their software is well worth registering.
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At least in the NewsGoups, there are regular uploaders and you get to learn who to trust and who has the best posts.
There are times when some of the groups do get flooded with Malware SPAM, but you can ignore it as this is easily recognizable even though it is a nuisance.
With UseNet, what is posted on one News (NNTP) server, propagates to all NNTP servers. But how much of that content actually reaches each server depends on how well that each server is connected to the internet, any network problems and the quality of the service itself plus the retention period of each server. So some servers will have everything while other servers will be missing lots of parts or even whole files. Retention period is how long a server is set to retain the post on that particular server.
This is why it is recommended to always use a Premium News Server as these servers are usually well connected, have long retention such as 100 to 200 days or more and the files will be complete unless there was a problem elsewhere in the propagation.
I hope this has been helpful.