Sophos experts note that since Facebook does not approve applications before they are made available on the site, users are often putting their trust in complete strangers when they choose to install the next application.† In this instance, there was nothing wrong with the recipient's profiles and the warning messages were in fact a viral attempt by a third party to recruit more users, and - potentially - steal personal information for financial gain.
Graham Cluley, senior technology consultant at Sophos commented:
Facebook applications are very popular and once all your friends have downloaded the latest must-have, it's very tempting to follow suit.
But, installing all applications sent your way, could open up serious holes in your security and allow hackers to gain access to your profile and the information stored on it.† Just like with other computing applications, it's essential to exercise caution when you're not sure of the origin - just because your friends have downloaded it, doesn't necessarily mean it's safe.
Source for the screenshots: AllFacebook.