When the Internet first caught on with the general public in the mid 1990s it was a relatively safe place. Since then some dangerous places have sprung up within it. With worldwide reach and virtual anonymity it has attracted many destructive, dishonest people. Some of them create viruses, worms, spyware, adware, keyloggers and the other forms of virulent, invasive code known as malware that cause computer problems. Some of them use this code and various techniques to secretly steal your identity by gaining access to your personal information!
Annoying pop-ups, machine slowdowns and PC crashes are often a result of malware. Hackers monitor Internet traffic and look for unprotected PCs that they can infect.
Even worse if your PC is compromised it can without your knowledge become a slave machine that further spreads these malware programs to other unprotected PCs!