There are many spyware and adware programs that can harm your computer. You have to be alert on the following signs of infection on your system.

Pop-ups with your name appearing on your desktop, even if you are not connected to the net and even when your browser is closed are a sure sign of spyware infection.

The change of your browser homepage, even if you reset it, is mostly caused by spyware.

If your Internet search bar is taking you to a different search engine, it is a definite sign spyware infection.

A mysterious appearance of browser toolbar repeatedly even after you have closed it is caused definitely by a spyware.

Appearance of new items on your favorites list, and disappearance of your old items can be an indicator of spyware infection.

If your computer system is running slowly and your task manager shows that you are running at 100%, this may be caused by a spyware. The most needed free space of system is consumed by the spyware and that is the cause of slow running.

If the lights on the modem are blinking and/or the network icon flashing on the screen, when there is no downloading or uploading. It shows that some spyware is transmitting data without your knowledge.

You may not find any above indications, but still there may a spyware I your system. So it is better to have a regular checkup.