Very nasty, I was on Firefox, doing a Google search for images of Sea Anenomes and the second choice ofter National Gegraphic came up with
anemone maxpedition - BC Photography -sea anemone brains. anemone flower picture. jewel anemone facts .... interesting facts about sea anemone. jewel anemone interesting facts. maria anemone ... bencoope.com/bftry/hxmj.php?s=624460
This brought up a window "Online Protection" "you are infected" and a long list of viruses, seeming to start to scan my computer and offering to download a solution.
Worse, when I tried to close the tab or close Firefox, it brought up a do you really want to close the scan window. I had to kill the process to get rid of this safely and even then it tried to reload at firefox restart.