How exactly does Mycelium backup work? You get 12 English words as backup key for your wallet. What is mechanism behind this? Where are private keys kept? How are they secured? How are they retrieved with 12 words?
Try this link
https://www.reddit.com/r/Bitcoin/comments/2ik8jq/mycelium_bitcoin_wallet_20_hd_is_out/Remember your private keys are kept on your phone and could be compromised. For ultimate security use Mycelium with a Trezor, that way your private keys are in the Trezor immune to malware.