Read this part of MLNK response. This is tells the whole story. If they get buyout offer with the premium they will sell the company. The statement below tells me that they are trying to prevent hostile take over. But willing to sell the company with the premium. Read this:
"Furthermore, the issuance of the Rights is not intended to prevent a transaction that is determined by the Board of Directors to be fair, advisable and in the best interests of all ModusLink stockholders".