After checkpoints there is little need to get data from a torrent file instead of the network itself, since it is likely a CPU or disk IO bound operation, not network speed.
Also with this other torrent file, there is no way for me (other than downloading the whole file and decompressing it) to recreate + verify it locally.
Network speed is an issue, that's why we are using a torrent. There are currently 14620 blocks between the end of this torrent and the end of the blockchain. Bitcoind should download about as fast as torrent does, but sadly it doesn't.
Bitcoind verifies this data when it imports it, just like when it verifies data it pulls off random network nodes. The only possible attack is a 50%+1, and if an attacker could pull that off they would do it on the main network, or more likely they would just mine half the coins instead.
EDIT: For clarity