SUNNYVALE, Calif. – After dropping to number two in 2014, pornography has returned as the number one threat vector for malware infection on mobile devices.

And it’s not just back on top. The threat in 2015 is more than twice as large as that noted last year, according to cybersecurity firm Blue Coat Systems Inc., jumping from 16.55 percent in 2014 to more than 36 percent this year — meaning 36 percent of links to malicious sites are found on adult content sites.

The data and analysis are contained in Blue Coat’s 2015 State of Mobile Malware Report, which notes the three top types of malware are ransomware, potentially unwanted software and information leakage.

According to the report, mobile ransomware has grown dramatically over the past year. While some varieties that run on Android devices cause little damage beyond convincing victims to pay the cyber hostage-taker, many have adopted more sophisticated approaches common to ransomware in the Windows environment.

“With the increased performance capabilities of modern smartphones, it was only a matter of time before more advanced cryptographic ransomware, such as SimpleLocker, started showing up on mobile devices,” said Dr. Hugh Thompson, chief technology officer and senior vice president at Blue Coat. “These threats render music files, photographs, videos and other document types unreadable while typically demanding an untraceable form of payment such as bitcoin and employing a strict time limit for payment before the files become permanently inaccessible to the owner.”

Potentially unwanted software generally exhibits behavior typical of “adware” or “spyware”: spying on users’ on-line activity and personal data or serving extra ads. Blue Coat researchers have seen a major shift in the volume of such malware in the traditional and mobile spaces as the number of junk mobile apps hosted on sites the researchers classify in this category has risen steadily.

This type of mobile app, notable for its dubious utility, frequently finds its way onto a mobile device through the use of deceptive advertising or other social engineering attacks designed to deceive the victim into installing the unwanted program.

Most people are unaware that apps on their mobile device may be watching them and reporting to a cyber puppet master on a 24/7/365 basis, Thompson said. Called “information leakage,” the data theft usually comprises an unnoticeable drip of the version of a phone’s operating system, the manufacturer, the specific app or browser being used and similar information. Typically, phones do not include system tools allowing users to see what data is leaving their devices. Leaky data is often openly revealed in the “User Agent” string.

As for the future?

Mobile payment systems are set to grow, and services including contactless payment methods will incorporate additional security features such as biometrics or two-factor authentication, according to Blue Coat. In addition, because manufacturers update mobile OSes infrequently, the market for third-party security solutions that can support both traditional PC and mobile platforms almost certainly will expand. Mobile carriers and handset makers are already working on plans to fast-track critical OTA updates to vulnerable devices, but the work is slow and it may be some time before this segment of the mobile market matures.