It’s not always easy to tell if your computer has been compromised. More than ever before, the authors of computer viruses, worms, Trojans and spyware are going to great lengths to hide their code and conceal what their programs are doing on an infected computer. That’s why it’s essential to follow the advice given in this guide: in particular, install Internet security software, make sure you apply security patches to your operating system and applications and backup your data regularly. It’s very difficult to provide a list of characteristic symptoms of a compromised computer because the same symptoms can also be caused by hardware and/or software problems. Here are just a few examples: Your computer behaves strangely, i.e. in a