That warning was sounded this week by Kaspersky Lab, which said that it had spotted variations of that attack being hosted on the official Google Chrome Web store. Some versions of the attack, which originated in Turkey, are customized to target Italian users of Facebook, while other variations target Latin Americans.
"Attacks such as these ones are getting very common," Fabio Assolini, senior security researcher at Kaspersky Lab, said via email. He blamed users for too often not exercising good sense when it comes to adding extensions to their browser. "They need to know that an extension can access everything you do in the browser, all the data, passwords and the websites visited, so it's very important to not install unknown extensions," he said. "The situation gets worse when the malicious extension is hosted in the official Chrome Web store, as we noticed in some attacks."
[ Are Gmail users entirely too trusting? Read Gmail Is Not A Privacy Problem. ]
As with the Android security model, the Chrome browser lists which permissions any Chrome extension will be granted should a user allow it to be installed. Assolini recommended that all Chrome users regularly review the extensions they have installed, as well as the permissions they'd been granted. "Avoid installing those asking [for too many] permissions to access personal data," he advised.
The fake Facebook video attack campaign isn't the first time users have been targeted by malicious Chrome extensions. A particularly large campaign was spotted last year that targeted people in Brazil -- where Chrome's installation base is now 65%, according to StatCounter -- via malicious extensions distributed by the Chrome Web store.
Assolini said there's a constant "cat and mouse game" between cybercriminals, who upload malicious extensions to the Chrome Web store and attempt to trick people into installing them, and Google, which removes the extensions whenever it learns they're there.
The Chrome extension security situation improved after June 2012, however, when Google updated Chrome to prevent it from running any extension that wasn't procured from the Chrome Web store, and required users to navigate to their browser's "extensions" page to add any extension. Google explained that it made the change because it doesn't have the ability to take down malicious items promoted on other websites, meaning hackers could have launched attacks that silently installed extensions that would then monitor all Web traffic and information flowing to or from a browser.
At the same time it announced that change, Google also revealed that it had begun scanning extensions for signs of maliciousness. "To help keep you safe on the Web, we have started analyzing every extension that is uploaded to the Web Store and take down those we recognize to be malicious," the company said.