Microsoft has been doing some research into all the recent cross-platform malware 1, 2, 3 that attacks Windows, Macs, and sometimes even Linux. The company has concluded that current attacks exploit third-party vulnerabilities in software on these platforms. There are two ways the malicious code is being delivered, according to the software giant: via the Web and via e-mail attachments.
via Microsoft: Windows, Mac malware gets in via Adobe, Java, Office | ZDNet.