Register at the above link to receive a voucher, which can be redeemed between 01/02/2011 and 01/05/2011.
Travel must be between 01/02/2011 and 01/08/2011.
Vouchers are only valid for itineraries where all flights are operated by Lufthansa, Lufthansa Italia and Lufthansa Regional Partner (incl. Lufthansa City Line and Eurowings).
Full Ts&Cs from the link