Microsoft conducted an interesting contest on the social-networking service Twitter this week, offering to give free Windows Phone handsets to the five Android users who provide the best stories about their malware problems on that platform.

"More malware on Android!" Microsoft evangelist Ben Rudolph wrote in a Twitter post, or tweet, on Monday. "Been hit? Share [your] ... story to win a [Windows Phone] upgrade."

Rudolph was then inundated by responses. He spent the rest of the day answering them and has closed the contest. No word yet on the, um, lucky winners.

Android, as you might know, is the most heavily victimized smartphone platform by far. In fact, in the most recent quarter, it was the only smartphone platform targeted by malware. And just this past week, Google removed 22 malware apps from its Android Marketplace.

Do you think Apple or Microsoft has ever removed that many malware-laden apps from their respective smartphone app stores? Ever?

And the security researchers that alerted Google to the malware apps now say they've found even more. Remember, these are in Google's own app store.

"Just this week there have been several waves of a new threat posted to the official Android Market," security firm Lookup noted in a blog post. "In the last week we have notified Google of 9 identical applications that were skinned to appear more appealing to potential users ... Google responded quickly to our reports and pulled these apps from the Android Market."

Good for Google. But why were these apps even in its Marketplace to begin with?

Of course, Microsoft is no stranger to malware. And even Windows Phone, which utilizes sandboxing techniques to isolate apps from each other and the OS, isn't perfect. This week, the software giant confirmed an issue with Windows Phone 7.x that could allow a carefully crafted SMS message to crash the OS, causing the phone to continually reboot. This issue has been misreported as "an attack," but it appears to affect more than SMS and probably isn't specific to Windows Phone.

"We are aware of the issue, and our engineering teams are examining it now," Microsoft Senior Product Manager Greg Sullivan said. "Once we have more details, we will take appropriate action to help ensure customers are protected."

Meanwhile, I do have some advice for Android users. The problem with Google's Android Marketplace is that it isn't curated or protected in any meaningful way by the online giant. And this means that it's bursting at the seams with apps both good and bad. Fortunately, the open nature of Android means that you have a lot of choice, and one of the choices you have is to use a different app store. If it's available in your area, and via your wireless carrier, I recommend using Amazon's AppStore for Android instead. This store is curated, meaning that every single app is tested by Amazon before being made available to the public. That means it's not as voluminous in terms of number of apps, yes, but also that the apps are generally a lot safer.