The Diet Adware is a dubious program, whose primary purpose appears to be the delivery of intrusive advertisements to users' computers. Besides being classified as adware, Diet also falls into the category of PUPs (Potentially Unwanted Programs), due to the questionable methods involved in its distribution. For example, infosec researchers have observed the threat being injected into ISO files downloaded from dubious sources.
Once activated, the Diet Adware could be responsible for the appearance of a constant stream of untrustworthy advertisements. The advertisements may take the form of pop-ups, banners, in-text links and more. Furthermore, advertisements generated by adware are highly unlikely to be promoting legitimate products or destinations. Instead, users could see advertisements for hoax websites, fake giveaways, phishing portals, platforms distributing additional PUPs, etc.
It also is important to keep in mind that most PUPs possess additional functions that could be silently running in the background of the system. The installed PUP may be spying on the user's browsing activities, harvesting device details, or even trying to obtain sensitive information from browsers' autofill data. All captured data could then be exfiltrated to a server under the control of the PUP's operators.