In general Apple supports the products they release with 2-3 OS upgrades. For example the iPod Touch 1st Generation came with iOS version 1 and can be upgraded to iOS version 3 but not past that, an iPod Touch 2nd Generation came with iOS version 2 and can only but upgraded to iOS 4. This means that those older devices may not receive updates that could enable new security features or security fixes. The iOS model does not suffer from the fragmentation problems that Android experiences with multiple manufacturers delivering multiple handsets.