The CVE Details has listed specifically which mobile operating systems have to fight with the most vulnerabilities. Apple iOS brings up an impressive 238 vulnerabilities in the time period 2007 to 2013 , 106 of them alone in the year 2012. These vulnerabilities expolit the device in such a way that it no longer works and the malicious code can be executed on the smartphone very easily. On the other hand, only 27 vulnerabilities have been found in the Android operating system so far with a downward trend.
The risk is still very high for the users of Android operating system because the vulnerabilities are exploited by much more malwares. Android malwares can spread themselves better through the weaker security checks on Google Play. The extra and significant security risks is also caused by installing the apps from illegal and unofficial App stores. A virus scanner on your Android smartphone is therefore very essential.