The entire philosophy of the two competing "App markets" are different.

The Android Market, known as **Google Play**, allows any submitted application. Apps aren't checked or pre-screened, they're simply submitted, and people can download them. Any kind of app can be submitted to the Play store, even one that hooks into the core operating system. Applications aren't run in a *sand box*.

This is a double-edged sword, as a developer can write a malicious app, one that steals your data, disables your phone, and other nasty things. Usually, only when enough people complain will Google take notice and remove an app.

Apps submitted to the **iOS App Store** have to go through a vetting process. Apple will inspect your app, to make sure it does what it says without bugs, doesn't use private or secret functions on the iOS device, and so on. Apps are run in a *sand box* and cannot make any major changes to the way the device works. Since all apps are pre-screened before they are posted on the App Store, there is almost no chance of an application being malicious (virus, data stealing, etc).

As for whether or not you actually *need* an anti-virus app or not, well, [this question][1] may help answer that. Personally, I don't think viruses are a massive threat yet, although they may be later. I'd be more worried about data-stealing apps, especially if the app holding sensitive data isn't sufficiently protected. [Last year, Skype wasn't encrypting its contacts database][2], and malicious apps were able to simply read the data. This has, since, been patched.


  [1]: http://android.stackexchange.com/questions/341/is-an-antivirus-really-needed-for-android
  [2]: http://www.androidpolice.com/2011/04/14/exclusive-vulnerability-in-skype-for-android-is-exposing-your-name-phone-number-chat-logs-and-a-lot-more/