Adware is mostly a free software that displays advertising banners while the program is running. The advertisements are displayed as a means to recover the software expenses or to generate revenue by developers. Although most of the adware programs are safe to use, but special care must be taken because these type of programs can also upload the specific user information to internet with explicit permission. So adware programs can also act as spyware. Make sure that the adware you are using is from a reputed company also carefully read any privacy agreements related to it.