Yes. Sigfox do offer a location feature depending on the calculation of the most proble location of the hardware device. Integrating this features would be a problem. Moreover, this feature is cost efficient too as no additional hardware is required.

If you have an Arduino with an inbuilt or external Sigfox modem, the only thing that you will need is to buy Sigfox connectivity. Without Sigfox modem,your device hardware will not be able to send Sigfox messages. Buying single Sigfox subscriptions can be a bit tricky though (depending on your local Sigfox operator and their partners) since Sigfox subscriptions generally are sold in batches of several thousand. That's why the Arduinos with bundled subscriptions exist.

The unique thing about this network is that there is no synchronization between base station and device. Instead, the device broadcast radio signals to multiple base stations close by through random frequency. This means that hackers would not be able to gain access into Sigfox network backend. Furthermore, there is a restricted downlink and devices chooses when to communicate and at which frequency, which protects it from hackers sending targeted malicious commands.

No. Sigfox devices do not have an IP address. They are not connected to the Internet. They cannot be used as a vector of attack of a global system. What happened with baby monitors (massive DDoS attack on Dynn servers) could not, by nature, happen through Sigfox devices. Sigfox devices can send 12 bytes at a time and receive up to 32 bytes a day >> downloading a malware on Sigfox device becomes impossible.

Through the unique Sigfox network design, the network availability is very high at 99.8% where there is coverage. As devices broadcast radio signals, multiple base stations within proximity are able to pick up these packets. Sigfox backend would then send only an instant of it to the destination set. Since there are multiple base stations around, in the event of a single failure, there are many others around to pick up the packets. The more base stations are installed, the more stable the network will be.