System Shock by Liam O'Donnell
"Daniel felt his bones creak and his body stretch as the System lost control of its programming..." In the year 2115, Daniel and Jack are lost in their favourite Virtual Reality game when suddenly the system crashes and the evil Azkar and an army of computer game scum take over the virtual world. Unable to get back to Realworld, the friends face being destroyed as the program is deleted, one data line at a time. Could a giant Owlbear, a deranged Cyborg, or even a girl save them before the Datwipe countdown hits zero?