Why did this pop up on Facebook?

[Ben]

I'm a guy. This window popped up when I was browsing through my pictures. It was a text box with a girls name and the text said "hi are you there?" I didn't reply and I got off my Facebook. It would have allowed me to type in the box. Why did this random girl start talking to me? It doesn't appear in my messages what she was typing.

[Alex]

That was not FB. Go get yourself some antivirus, I've seen that chat box before and clicking on it resulted in a very nice collection of malware being downloaded. My AV stopped it, but you seem to have already been infected with the virus.

[Daniel]

That Was Not From Facebook its Just a Random Pop Up Ad Just Close it Its a Advertisement