Most computer users would not knowingly spread malware, so hackers must use stealth methods to install the software. One example of a brute force attack is bots that search the internet for computers with unpatched operating systems that can be used a backdoors through which malware is installed. One of the most common methods of installing malware is tricking the user through a phishing attack. Malware is often installed when a one receives an infected file from a trusted source downloads it, then and forwards or shares it. Once malware is installed on a computer, it can cause damage by stealing or encrypting data, or the malware can control the computer for its own purposes. One of the attacks on web sites is a denial-of-service attack. This finds malware that has been installed on many computers sending requests to a particular server at a particular time. The server becomes overwhelmed and goes offline. These attacks would not be possible without many malware-infected computers.