According to F-Secure, a security firm, Android accounted for 79% of all mobile malware in 2012. This is an increase of 66.7% and 11.25% for 2011 and 2010, respectively. Apple's iOS doesn't even attempt to come close to these numbers, and only accounted for 0.7% of mobile malware in 2012.
Windows Mobile, Blackberry and Symbian all entered the pie with much less than Android, with 0.3%, 0.3% and 19%, for Windows Mobile, Blackberry and Symbian, respectively. The security firm also discovered that Android saw a surge in malware at the end of the year, but most of the malware is found in emerging markets. This means that most, not all, people in Europe and the US won't be affected, but everyone should always play it safe when opening up messages, links and emails.