Is it a security risk?
Yes, it absolutely is. The Bitcoin client will not check that the blocks are valid if they are downloaded in this way. 
Topic: High speed Blockchain Download - page 2. (Read 2742 times)
I was sick of waiting 24hours for blockchains to download so I have uploaded one for all to download.
Blockchain is available here:
http://ul.to/oq00jvjo
Instructions available here:
http://goo.gl/Y69yF
Just download and copy files into datadir.
Is it a security risk?
No. Just so long as you let the rest of the blockchain download on top of it. Would be impossible to create a blockchain that was fake that could have real blocks linked on top of it. Just check that the number of blocks in the client matches the number here http://blockexplorer.com/q/getblockcount .
If service is well used will update daily.
Sorry file is very large so can not host for free - downloader pays if they want a high speed download - but you can pay in bitcoins!
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