For those using Microsoft Internet Explorer, the LizaMoon software shows a link to pop up to a fake anti-virus product which claims to have found security threats on the user's computer. Once downloaded, the user is then prompted for payment to purchase the fake software.
Facebook scams - such as the ones that promise to reveal who has looked at your profile, only to source users' personal data - were the third most common threat last year.
The report also warned against using online pharmacies as there was a good chance the products were not what they were claimed to be.
Cybercriminals also used the popular Angry Birds game to hook in victims.
AVG Technologies found a Trojan-infected version of the app called Angry Birds Space uses the same icon and graphics.
The fake app fools users by making them think its the real thing and "will therefore be less likely to become aware of its sinister activities", the AVG report said.
Michael McKinnon, security adviser at the company, said it was vital for consumers to think before they clicked "OK" to anything online or on their phone.
BE CYBER-SAFE
* Before installing an app, do a background check and download only from stores or sites you trust.
* Think before you click 'OK' to any requests.
* Keep your computer programs up to date so you are not tempted to follow prompts to upgrade.
* Install antivirus security software on your computer and your smartphone.
* Monitor your mobile phone bills.