Explanation:

A computer is fundamentally 'A device which is able to store data' (1) and 'A device which is able to analyse data' (2). These are core capabilities. Statement (3) 'A device which is able to maintain full security' is incorrect; security is a complex system of software, hardware, and user practices, not an inherent ability of the computer itself. Statement (4) 'Sometime attacked by virus' describes a vulnerability, not a defining characteristic or positive function. Therefore, only statements 1 and 2 accurately describe fundamental aspects of a computer's capabilities, making option (a) '1 and 2' the correct choice.