Check Point researchers discovered another widespread malware campaign on Google Play, Google’s official app store. The malware, dubbed “Judy”, is an auto-clicking adware which was found on 41 apps developed by a Korean company. The malware uses infected devices to generate large amounts of fraudulent clicks on advertisements, generating revenues for the perpetrators behind it. The malicious apps reached an astonishing spread between 4.5 million and 18.5 million downloads. Some of the apps we discovered resided on Google Play for several years, but all were recently updated. It is unclear how long the malicious code existed inside the apps, hence the actual spread of the malware remains unknown.

We also found several apps containing the malware, which were developed by other developers on Google Play. The connection between the two campaigns remains unclear, and it is possible that one borrowed code from the other, knowingly or unknowingly. The oldest app of the second campaign was last updated in April 2016, meaning that the malicious code hid for a long time on the Play store undetected. These apps also had a large amount of downloads between 4 and 18 million, meaning the total spread of the malware may have reached between 8.5 and 36.5 million users. Similar to previous malware which infiltrated Google Play, such as FalseGuide and Skinner, Judy relies on the communication with its Command and Control server (C&C) for its operation. After Check Point notified Google about this threat, the apps were swiftly removed from the Play store.

Figure 1: A malicious Judy app on Google Play

How Judy operates:

To bypass Bouncer, Google Play’s protection, the hackers create a seemingly benign bridgehead app, meant to establish connection to the victim’s device, and insert it into the app store. Once a user downloads a malicious app, it silently registers receivers which establish a connection with the C&C server. The server replies with the actual malicious payload, which includes JavaScript code, a user-agent string and URLs controlled by the malware author. The malware opens the URLs using the user agent that imitates a PC browser in a hidden webpage and receives a redirection to another website. Once the targeted website is launched, the malware uses the JavaScript code to locate and click on banners from the Google ads infrastructure.

Upon clicking the ads, the malware author receives payment from the website developer, which pays for the illegitimate clicks and traffic.

The JavaScript code locates the targeted ads by searching for iframes which contain ads from Google ads infrastructure, as shown in the image below:

Figure 2: Searching for iframes containing Google ads

The fraudulent clicks generate a large revenue for the perpetrators, especially since the malware reached a presumably wide spread.

Who is behind Judy?

The malicious apps are all developed by a Korean company named Kiniwini, registered on Google Play as ENISTUDIO corp. The company develops mobile apps for both Android and iOS platforms. It is quite unusual to find an actual organization behind mobile malware, as most of them are developed by purely malicious actors. It is important to note that the activity conducted by the malware is not borderline advertising, but definitely an illegitimate use of the users’ mobile devices for generating fraudulent clicks, benefiting the attackers.

In addition to the clicking activity, Judy displays a large amount of advertisements, which in some cases leave users with no option but clicking on the ad itself. Although most apps have positive ratings, some of the users have noticed and reported Judy’s suspicious activities, as seen in the images below:

Figure 3: Comments made by suspicious users

As seen in previous malware, such as DressCode, a high reputation does not necessarily indicate that the app is safe for use. Hackers can hide their apps’ real intentions or even manipulate users into leaving positive ratings, in some cases unknowingly. Users cannot rely on the official app stores for their safety, and should implement advanced security protections capable of detecting and blocking zero-day mobile malware.

Appendix 1 – list of malicious apps developed by Kiniwini

Package name App name Date Min Max air.com.eni.FashionJudy061 Fashion Judy: Snow Queen style 24.3.17 100,000 500,000 air.com.eni.AnimalJudy013 Animal Judy: Persian cat care 14.4.17 100,000 500,000 air.com.eni.FashionJudy056 Fashion Judy: Pretty rapper 24.3.17 50,000 100,000 air.com.eni.FashionJudy057 Fashion Judy: Teacher style 24.3.17 50,000 100,000 air.com.eni.AnimalJudy009 Animal Judy: Dragon care 14.4.17 100,000 500,000 air.com.eni.ChefJudy058 Chef Judy: Halloween Cookies 10.4.17 100,000 500,000 air.com.eni.FashionJudy074 Fashion Judy: Wedding Party 7.4.17 50,000 100,000 air.com.eni.AnimalJudy036 Animal Judy: Teddy Bear care 16.4.17 5,000 10,000 air.com.eni.FashionJudy062 Fashion Judy: Bunny Girl Style 24.3.17 50,000 100,000 air.com.eni.FashionJudy009 Fashion Judy: Frozen Princess 7.4.17 50,000 100,000 air.com.eni.ChefJudy055 Chef Judy: Triangular Kimbap 10.4.17 50,000 100,000 air.com.eni.ChefJudy062 Chef Judy: Udong Maker – Cook 10.4.17 10,000 50,000 air.com.eni.FashionJudy067 Fashion Judy: Uniform style 24.3.17 10,000 50,000 air.com.eni.AnimalJudy006 Animal Judy: Rabbit care 14.4.17 100,000 500,000 air.com.eni.FashionJudy052 Fashion Judy: Vampire style 24.3.17 100,000 500,000 air.com.eni.AnimalJudy033 Animal Judy: Nine-Tailed Fox 18.4.17 100,000 500,000 air.com.eni.ChefJudy059 Chef Judy: Jelly Maker – Cook 10.4.17 50,000 100,000 air.com.eni.ChefJudy056 Chef Judy: Chicken Maker 10.4.17 50,000 100,000 air.com.eni.AnimalJudy018 Animal Judy: Sea otter care 14.4.17 100,000 500,000 air.com.eni.AnimalJudy035 Animal Judy: Elephant care 16.4.17 5,000 10,000 air.com.eni.JudyHappyHouse Judy’s Happy House 10.4.17 100,000 500,000 air.com.eni.ChefJudy036 Chef Judy: Hotdog Maker – Cook 29.3.17 50,000 100,000 air.com.eni.ChefJudy063 Chef Judy: Birthday Food Maker 10.4.17 50,000 100,000 air.com.eni.FashionJudy051 Fashion Judy: Wedding day 20.4.17 100,000 500,000 air.com.eni.FashionJudy058 Fashion Judy: Waitress style 24.3.17 10,000 50,000 air.com.eni.ChefJudy057 Chef Judy: Character Lunch 10.4.17 100,000 500,000 air.com.eni.ChefJudy030 Chef Judy: Picnic Lunch Maker 10.4.17 500000 1000000 air.com.eni.AnimalJudy005 Animal Judy: Rudolph care 14.4.17 100,000 500,000 air.com.eni.JudyHospitalBaby Judy’s Hospital:pediatrics 10.4.17 100,000 500,000 air.com.eni.FashionJudy068 Fashion Judy: Country style 24.3.17 10,000 50,000 air.com.eni.AnimalJudy034 Animal Judy: Feral Cat care 16.4.17 10,000 50,000 air.com.eni.FashionJudy076 Fashion Judy: Twice Style 20.4.17 100,000 500,000 air.com.eni.FashionJudy072 Fashion Judy: Myth Style 20.4.17 50,000 100,000 air.com.eni.AnimalJudy022 Animal Judy: Fennec Fox care 14.4.17 100,000 500,000 air.com.eni.AnimalJudy002 Animal Judy: Dog care 14.4.17 100,000 500,000 air.com.eni.FashionJudy049 Fashion Judy: Couple Style 24.3.17 100,000 500,000 air.com.eni.AnimalJudy001 Animal Judy: Cat care 14.4.17 100,000 500,000 air.com.eni.FashionJudy053 Fashion Judy: Halloween style 7.4.17 100,000 500,000 air.com.eni.FashionJudy075 Fashion Judy: EXO Style 7.4.17 50,000 100,000 air.com.eni.ChefJudy038 Chef Judy: Dalgona Maker 28.3.17 100,000 500,000 air.com.eni.ChefJudy064 Chef Judy: ServiceStation Food 10.4.17 10000 50000 air.eni.JudySpaSalon Judy’s Spa Salon 10.4.17 1,000,000 5,000,000 Total 4,620,000 18,420,000

Appendix 2 – list of apps developed by other developers

Package name App name Date Min Max Developer com.CoupleDday 커플디데이 (커플기념일, 위젯) 2-Apr-17 100,000 500,000 Neoroid com.DogSound Dog Music (Relax) 29-Jun-16 10,000 50,000 Neoroid com.kakaotalkchatanalyst.ks 카카오톡 대화분석기 25-Feb-16 1,000,000 5,000,000 DeepEnjoy com.PeriodCalendar 황금기 알리미 (여성달력) 20-Apr-16 100,000 500,000 Neoroid com.MoneyBook 100억 가계부 2-Apr-17 100,000 500,000 그린 스튜디오 com.lee.katocpic KatocPic(카톡픽) – 카톡프로필 23-Aug-16 5,000 10,000 Wontime com.appnapps.app77 필수추천 무료어플 77 5-Feb-17 1,000,000 5,000,000 App&Apps com.sundaybugs.spring.free Spring-It’s stylish, it’s sexy 30-Sep-16 1,000,000 5,000,000 Sundaybugs com.lx5475.craftingbox2 Crafting Guide for Minecraft 4-May-17 500,000 1,000,000 JIZARD Total 4,215,000 18,060,000

Appendix 3 – list of SHA256

a7e2030649cca0651730d4bea6f9c03200aaa3a0da56f112bf7c5691c172fcde

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0f883861ce387f2e6336f68f040a6bb635fe8358b9eb6efe1398f887000a9351

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