In a very uninformative statement, Tandem Computers Inc said yesterday that it had agreement in principle to acquire Atalla Corp, a privately held San Jose, California systems house specialising in secure transaction systems for financial and retail markets. No details either of terms or of the size of 15- year old Atalla were given. The firm builds security cystems for customer identification, card management, electronic payments, network interchange and computer security, and has more than 1,500 customers. It also holds numerous patents on its security products. It will be run as a wholly owned subsidiary of Tandem in its present location. It has offices in the US, Canada, Eur-ope, South America and Australasia.