Date Added: Mar 2011
In this paper there is discussed relation between seemingly independent aspects of software quality - security and usability. This relation is demonstrated in case study of password authentication. For this purposes a method of password security is suggested and described in this paper. This method consists in mathematical model of dictionary attack and brute force attack. This model is used to break passwords gained from two studies. In these two studies different groups of end users were instructed to select a password by a different way.