Warning! Fireball Malware
Security researchers have discovered a massive malware campaign that has already infected more than 250 million computers across the world, including Windows and Mac OS.
Dubbed Fireball, the malware is an adware package that takes complete control of victim's web browsers and turns them into zombies, potentially allowing attackers to spy on victim's web traffic and potentially steal their data.
Read more at The Hacker News website, the popup you get should only be an offer to subscribe to their newsfeed.
So far, this malware is pretty easy to get rid of... (Famous last words).
"To remove the adware, just uninstall the respective application from your computer (or use an adware cleaner software) and then restore/reset your browser configurations to default settings."