Spammers and hackers continued to make Android their primary target last quarter, when nearly all new mobile malware was aimed at the open source operating system, according to a new report from Intel-owned security firm McAfee Labs.

The quantity of malware targeted at Android jumped nearly 37 percent between the second quarter and the third quarter, McAfee said.

"The Symbian OS (for Nokia handsets) remains the platform with the all-time greatest number of malware, but Android is clearly today's target," McAfee said in its report.

Some of the most common security threats were Trojan viruses that sent out text messages, collected personal information and stole money. Two new malware apps stole information by recording users' phone calls, and others used root exploits to read system files containing information about text messages, e-mails and contact lists.

Android has been an easy target for spammers and hackers because apps for the open source platform can be downloaded from third parties with lax vetting policies, and Google historically has been less vigilant about malware than Apple.

An overall increase in spam and viruses prompted McAfee to increase its forecast for the amount of malware on the market from 70 million unique samples by the end of 2011 to 75 million unique malware samples, making this year the busiest in malware history.

"This has been a very steady quarter in terms of threats, as both general and mobile malware are more prevalent than ever," said Vincent Weafer, senior vice president of McAfee Labs, in a statement.