Here's how to locate it malware on your device and remove it.
Remove infected apps from Google Play
The main source of infection was the 9Apps app store. But also Google Play Store seems to have been affected by malware. OR Check Point discovered 11 applications that contained a "malicious but inactive" set of files related to Agent Smith. Agent Smith versions discovered on the Google Play Store used a slightly different dissemination technique, but had the same end goal. After Check Point reported to Google, all these apps were removed from the Google Play Store.
How to locate and remove Agent Smith?
Locating Agent Smith on your device is not difficult. If you notice that the apps you use usually start suddenly showing a large volume of ads before they did not, it's a sign that something is wrong. Also, if you're having difficulty or can not even get out of an ad, it's still a sign of malware. However, as well malware is quite distinct in his movements, it is very difficult to locate the subtle changes he makes in one application.
Of course, the sudden appearance of a large volume of ads in an application is not necessarily a sample of that malware, as there are other malware that use similar techniques. Your device may be infected with something else.
If you suspect that something is wrong with your device, it is advisable to do an antimalware or antivirus scan to detect if any malware exists.
For this purpose, you can use Malwarebytes Security, the excellent version of Android tool to fight malware. Download Malwarebytes Security and run a full system scan. This should detect and remove malicious applications.