AdF.ly is a URL shortener similar to shorte.st that gives the user money when the user shortens a link with it, but the ads displayed may install adware and spyware in the user's computer, and it can fill the user's computer with popups. This can be avoided if the user simply clicks the "skip ad" button and quickly closes the window, or doesn't click the ad at all. It also sometimes links to scams, like the Brit method.
If the user uses an ad blocker, it will keep telling the user to deactivate their ad blocker until the user turns it off. Sometimes it can also result in taking longer to skip the ad.