Security researchers discovered more than 32,000 fraudulent Black Friday apps in the wild, many of which use the branding of the top five U.S. online retailers to spread malware and steal customer credentials.

According to RiskIQ’s “2017 Black Friday E-Commerce Blacklist,” which was derived from a data set of 2 billion daily HTTP requests, 20 million mobile apps, 300 million domain records and 783 locations across more than 100 countries, about 1 in 25 Black Friday apps available in global app stores are malicious. Researchers also discovered at least 15 fraudulent apps that use the branding of the top five online retail companies to dupe users into divulging their sensitive data.

App Store Security Is Not Bulletproof

Black Friday is a huge day for e-commerce. According to the RiskIQ report, in 2016 154 million consumers did their Black Friday shopping online, spending $5.27 billion, which represented a 17.7 percent increase year over year. Mobile revenue alone totaled $1.2 billion, representing a growth rate of 33 percent year over year. Overall, nearly 40 percent of sales occurred on a mobile device during last year’s Black Friday weekend.

The report found that even some of the most popular app stores featured malicious Black Friday apps. The Google Play store hosted the largest number of fraudulent apps, while Apple’s App Store contained 85 legitimate apps that had been infected with malware despite rigorous security testing. The report pointed out that although most official mobile app stores have relatively strong verification processes in place, these systems are “not bulletproof.”

While the volume of blacklisted apps declined by 40 percent from Q1 to Q2 2017, suggesting a global boost in security awareness, these apps still put less savvy online shoppers and retailers at risk of fraud during the holiday shopping season.

Avoiding Fishy Black Friday Apps

To mitigate the risks from these malicious apps, RiskIQ advised users to avoid downloading applications that request questionable permissions to access data such as contact lists, text messages, administrative features, stored passwords and credit card information. Users should also be wary of app developers who use free email services such as Gmail.

The most obvious and important takeaway from the report is that consumers must be particularly proactive about their online security during the bustling holiday season.