This is how the "3 People Unfriended" advertisement looks:

Is it that persons who have seen the advertisement social networking accounts were hacked? No. Do not be fooled by the advertisement. The advertisement is not able to tell how many people unfriended you. It is just an advertisement with the text or banner “3 People Unfriended You” that the advertiser uses to lure curious website visitors into clicking on his/her ad.
Some advertisers, like this one, use deceptive techniques to drive traffic to their websites. So, when you see a suspicious advertisement like this one, do not let your curiosity lead you astray. A few persons have claimed that their antivirus software blocked this web address m.exfriendalert.com indicating that the malware Mal/HTMLGen-A was found, after clicking on the advertisement.