Downloading free screensavers and wallpapers poses a threat to a computer since freeware often includes unwanted software that is either annoying or harmful. The threats include viruses, adware, spyware and unwanted browser add-ons.
To avoid putting a computer at risk, download only from trusted and verified sources. Even when downloading from a trusted source, read carefully throughout all the installation screens since sometimes the installation wizard asks for permission to install additional software and browser add-ons.
Because some viruses can be concealed within free software installation files, it's important to scan a downloaded installation file for viruses before executing it.