Three days ago I sent a payment via my MultiBit wallet but it is still marked as unconfirmed, only 4 confirmations. How long it will take this transaction to become fully confirmed? Thanks.
Bitcoin transactions are almost instant. Average confirmation time is around 8 minutes, but first confirmation may take an hour and eight confirmations even more. Thing is there is no such thing as fully confirmed transaction. The receiver of bitcoin transaction may decide not accept the transaction before certain amount of confirmations are done to prevent double spending. Bigger transaction fee will increase the transaction confirmation priority, so if you did not pay any transaction fee the confirmations may take quite a while.
Just reset blockchain in the multibit menu. If it doesn't help, you can export private key from the address the tx has been made from, import it on blockchain.info and doublespend it to your own address.