Tata Sons on Thursday hit back at ousted chairman Cyrus Mistry saying his letter lambasting his predecessor Ratan Tata makes unsubstantiated claims and malicious allegations."It is a matter of deep regret that a communication marked confidential to Tata Sons board members has been made public in an unseemly and undignified manner. The correspondence makes unsubstantiated claims and malicious allegations, casting aspersions on the Tata group, the Tata Sons board and several Tata companies and some respected individuals," a Tata Sons statement here said."These will be responded to in an appropriate manner," it added.Cyrus Mistry's email on Tuesday to directors of Tata Sons, a day after they voted to remove him as Chairman, contains allegations of "aggressive accounting" and fraudulent payments, and warns of potential write downs of losses of $18 billion at five group companies."It will be beneath the dignity of Tata Sons to engage in a public spat with regard to the several unfounded allegations appearing in his leaked confidential statement," the Tata Sons statement said."There is a multitude of records to show that the allegations made by Cyrus Mistry are unwarranted and these records will be duly disclosed before appropriate forums, if and when necessary, sufficiently justifying the decision made by responsible Boards of Directors," it added.