Generally a spyware program is installed on a PC using one of the following primary techniques.

Cheat to install

The user unintentionally installs the program by clicking on a link, which actually is attached to the installation of an executable file.

Pretend to install

Sometimes Spyware installation may appear as an innocuous dialog box. However, any attempt to close the box by clicking the close button will actually trigger Spyware installation. In fact, if this situation occurs, the end user is left with no choice but? to restart the system. An empty window with a title bar is a variation of the dialog box trap, where the spyware gets installed when the user tries to close the window.

Bundle to install

Additionally, adware and Spyware might be bundled with freeware programs. For example, many of the free file-sharing programs include some form of spyware which is installed when the user attempts to install the original freeware program. Many user agreements for freeware will alert you to the fact that a Spyware program is part of the download, but most users don't take the time to read the fine print.

Vicious to install

Some special hackers come into your PC with high technology. It is called malicious software. This form is not very common to personal computer, while the company computer often gets in troubles.
Once installed, spyware can transmit sensitive information as long as the user remains online. Also, once the spyware establishes itself in a PC, it is especially difficult to completely remove its effects.