Mobile device malware infections reached an all-time high last year, according to a new Nokia Threat Intelligence Report, released Monday.

Smartphones were by far the most vulnerable devices, with infections that rose nearly 400% in 2016. Attacks on smartphones represented 85% of all mobile device infections in the second half of the year, according to the report.

“From these trends, it is clear that cybercrime is moving to the mobile space and that smart phones are becoming the target of choice,” the report stated. The report examined trends and statistics for malware infections in devices connected through mobile and fixed networks in the second half of 2016, aggregating data from more than 100 million devices worldwide that use its Nokia NetGuard Endpoint Security solution.

In October 2016, malware infected 1.35% of all mobile devices–up from 1.06% in April 2016, and representing the highest level measured since reporting started in 2012, Nokia noted.

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Androids were by far the most commonly attacked smartphones: These devices were responsible for 81% of malware infections in the second half of 2016, up 95% from the year before. Windows/PCs followed, representing 15% of attacks, as they connect to mobile networks via USB dongles, mobile Wi-Fi devices, and smartphone tethering. iPhones and other mobile devices made up just 4% of attack victims, the report found.

The report also dove into the Mirai botnet and the DDoS attacks associated with it, calling it “the biggest security event of 2016.” The incident demonstrates the many vulnerabilities that still exist within the Internet of Things (IoT), and the necessity of building in and adding security measures to manage these devices.

“The security of IoT devices has become a major concern,” said Kevin McNamee, head of the Nokia Threat Intelligence Lab, in a press release. “The Mirai botnet attacks last year demonstrated how thousands of unsecured IoT devices could easily be hijacked to launch crippling DDoS attacks. As the number and types of IoT devices continue to proliferate, the risks will only increase.”

Nokia’s findings echo those of Kaspersky Lab, which in February found that the number of malicious installation packages hit more than 8.5 million–three times more than the year before. That report also found that ransomware and IoT attacks continue to rise.

As more people use their devices for both work and personal use, it’s more important than ever to ensure that business users take precautions to keep their devices secure and protect both personal and professional accounts. Running anti-malware on your devices, keeping software updated, and training employees on cybersecurity hygiene are all good places to start.

The 3 big takeaways for TechRepublic readers

1. Mobile device malware infections reached an all-time high in 2016, with smartphone infections rising nearly 400%, according to a new Nokia Threat Intelligence Report.

2. Android phones were the most vulnerable, representing 81% of malware infections in the second half of 2016.

3. The Internet of Things (IoT) represents a growing area of security concern, after the Mirai botnet demonstrated how these devices can be used to attack individuals and businesses.