As per the report, cyber criminals posted advertisement on websites which got mixed with legitimate ads possibly "due to lack of proper vetting when submitted by ad networks".
When users click on these malicious advertisement, they "exploited vulnerabilities on site visitors' computers to drop malware."
Malwares can steal details, password of users and even control entire device on which they get planted.
"Adware is the top threat in the mobile phone category. Although Trend Micro has identified a mammoth five million Android threats to date, it is predicting this will rise to eight million by the end of this year," the report said.