possible virus?

[kujo]

After many years of pcs my family recently switched to macs. Am new to this forum and looking for help. My teenage son was using google chrome to search the web and after visiting a site he probably shouldn't have, now has a message from the "international cyber security protection alliance". This seems like a virus? What do I do to remove this? Thanks in advance for all help!

 

[Slydude]

Give these directions a read. They explain how the scam works and how to get rid of it. If the directions don't make sense give the video a look see.