Int. J. Internet Technology and Secured Transactions, Vol. 2, Nos. 1/2, 2010 109 Copyright © 2010 Inderscience Enterprises Ltd. Security of internet-connected computer networks I. Tutănescu and E. Sofron Department of Electronics, Communications and Computing, University of Piteşti, Târgul din Vale Str., No. 1, Postal Code 110040, Piteşti - Argeş, Romania E-mail: tutanescu@upit.ro E-mail: sofron@upit.ro M. Ali* Department of Computer Science and Electronic Engineering, School of Technology, Oxford Brookes University, Wheatley Campus, Oxfordshire, OX33 1HX, UK E-mail: mali@brookes.ac.uk *Corresponding author Abstract: The security of computer networks connected to the internet is an important, vital and hotly contested real-world issue. Once the computer networks get connected to the internet, the number of attacks, their strength and intensity grow exponentially. All the attacks then exploit breaches in the network security. In this paper some of the passive and active attacks against the computer networks are presented. The anatomy of the attack is presented showing the phases and the techniques for penetrating into the computer networks – with the purpose to stress and highlight the several dangers faced by the network manager and the utmost necessity of setting a proper corporate network security policy in place. The detection of an attack is a difficult task because the detection technology is still in its infancy and has yet to mature, also once the attack is detected, the attacker in most cases still remains unknown. After the detection of the attack, the analyst needs some time to establish the actual nature of the attack. Keywords: internet-connected computer network; security breaches; incident; attack; detection; security policy; digital signature. Reference to this paper should be made as follows: Tutănescu, I., Sofron, E. and Ali, M. (2010) ‘Security of internet-connected computer networks’, Int. J. Internet Technology and Secured Transactions, Vol. 2, Nos. 1/2, pp.109–121. Biographical notes: Ion Tutănescu received his PhD in Electronic Engineering from the University of Piteşti, Romania, with a dissertation on increasing radio communications security. He is an Associate Professor of Computer Networks and Communications Security at the Department of Electronics, Communications and Computing - University of Piteşti. His research interests include communications, computer networks and information security.