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Two main things come to mind. First, like jimlynch said, the desktop/laptop market isn't dominated by PCs the way it used to be. Now there are a much higher percentage of machines running Mac OS and probably Linux as well than there was a few years ago. This makes those non-Windows machines more tempting targets for malware writers, who want to get as much from their efforts as they can. When only 5% of machines are running a particular OS, it did make a lot of sense to make as much effort as you would to go after 95% of machines. Another thing is that cross platform use of Java makes it so the same attack vector can be used for multiple operating systems- a malicious Java applet. Thanks, progress. It makes sense to me that you would want to get the most bang for your buck whether you are writing legit code or malware.