The Google scanner that checks apps for malware before they are installed on an Android smartphone or tablet has a detection rate that falls far behind that of third-party anti-virus products, a new study shows.

Researchers at North Carolina State University wanted to know whether additional antovirus software was necessary, in light of the Google service that is included in Android 4.2 Jelly Bean, the latest version of the operating system. What they found was a service in need of improvement.

Out of more than 1,200 malware samples, the Google scanner detected 193 for a "low detection rate of 15.32 percent," according to the study.

Antivirus software needs to have a rate of more than 80 percent to be considered at least good, Xuxian Jiang, an associate computer science professor at NCSU who led the research, said.

The next step was to test Google VirusTotal, a free online service that can check individual files and URLs for malware. The service uses limited versions of the antivirus engines of multiple vendors.

The results were only slightly better with a detection rate of 20.41 percent. In both tests, the research team used malware samples from the Android Malware Genome Project, an NCSU-led initiative to categorize the malware. The devices used were Nexus 10 tablets running Android 4.2.

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The Google scanner is designed to check apps downloaded from marketplaces other than Google Play. A weakness is in the limited amount of identifying data the service collects on an app in order to see if it matches malware traits in a Google database.

The information collected includes the app name, size and version; the URL associated with the app and the SHA1 value. SHA1 is a cryptographic hash function designed by the National Security Agency.

Cybercriminals can easily bypass this mechanism by repackaging malware or mutating it. To make the service more effective, Google would need to gather more information, such as uploading the whole app to its server for analysis, Jiang said.

However, this would cause unacceptable delays for many Android users. In addition, gathering more information inevitably raises privacy concerns.

"It really requires a very delicate tradeoff," Jiang said Tuesday. Google seems to be erring on the side of caution in data gathering.

"So far, too little information has been used," Jiang said. "Google has been very cautious in trying to avoid triggering user concerns on privacy."

Rather than do all analysis on a remote server, Google could add some detection capabilities on the Android device to improve the service, Jiang said. In addition, VirusTotal would be integrated into the server-side analysis to improve detection rates.

Not everyone believes antivirus apps are needed on Android devices, if users are careful to download apps only from trusted marketplaces, such as Google Play, and avoid clicking on unknown links in email and text messages.

Gartner has a long-standing position that antivirus software is not very effective and can degrade device performance. The analysis firm believes Google should vet apps before they are made available.

Jiang said he believes antivirus technology is needed because a large number of people outside of the U.S. download apps from marketplaces other than Google Play, increasing the risk of installing malware.

In addition, if security requires people to limit the number of apps they use, the value of the smartphone or tablet is diminished, because users cannot fully extend its features, Jiang said.

"If the user just buys the phone and never uses any additional apps and never clicks any untrusted links, then likely he will not need any [antivirus] solutions," Jiang said.

Most experts believe mobile malware is still at the beginning stages. However, the technology is maturing and the number of malicious apps continues to grow. In a 2013 trend report released Tuesday, security vendor ESET found that the number of unique malware soared 17 times globally this year, when compared to 2011.

The number is expected to rise "much more rapidly in 2013," the report said.