Spyware intentionally disables security software

Plenty of Spyware is poorly written and prone to crashing, often locking up the user’s machine.
Some Spyware intentionally disables security software like firewalls and anti-virus programs.
Remote Administration Tools (RATs) often allow intruders to shut down or restart the user’s computer.
Uses a modem-connected phone-line to call pay-per-minute phone services or phone-based payment lines
Programs called dialers can use a phone connected to the user’s computer to call adult pay-per-minute phone services
Certain pornographic websites allow patrons to pay their monthly fee by using a dialer program
Dialers can be automatically installed by certain websites using ActiveX scripts
Exploits a security vulnerability in another program
Many legitimate applications have loopholes or flaws in their code that hackers exploit for a variety of reasons.
Security exploits are often used to access a user’s computer and gain remote influence.
Some hackers attack security vulnerabilities purely for recognition or to point out flaws in a respected application.
Floods an Internet connection or network
Flooder programs send massive amounts of data to a computer or network in an attempt to overload and disable the connection.