In some cases, the error is a simple one: they do not really scan the app code. AV comparisons found that only use the app whitelists or blacklists, and sometimes very broad on it. They can allow any apps whose package files start with "com.instagram", but it would be trivial to create cut apps that used a variant on that name.
The apps that passed the mosquitoes came from well-known security brands, with big names like AVG, Kaspersky, McAfee and Symantec capturing everything. However, those who became short had a familiar pattern. Many of them were written by amateurs, cookie-cutter apps or from companies that clearly did not focus on security. Anti-malware apps from 32 of the suppliers in the test have disappeared during the two months since the test took place in January.
It is safe to say that this serves as a reminder to stick to antivirus tools from companies with solid track records. However, this also illustrates the challenge Google and other store operators face in screening apps. They can verify that the device does not harm the users or violate the law, but they cannot apply a basic level of quality needed to keep the phone safe.