I opened an internet radio app, HiDef Radio, that I have used before, many times, on my iPhone 4s with iOS 9.3. After connecting to a station and listening a short while, a window popped open saying:
(6) virus detected on your iPhone!
IP address 184.108.40.206 (not my iPhone's IP address)
One of the last sites you've visited contained a Trojan, loading via the vulnerabilities of the browser.
Click ok to start the cleaning process. After clean up, make sure to upgrade your system to the latest version.
Detected by Apple Firewall Ver 6.2.7
Clicking the Cancel button took my to the App Store for a VPN program, HotSpot Shield Free VPN Proxy which, as it turns out, I already have on my iPhone! But it was not running (and is not now, either) when the popup window appeared.
So what does all this mean? Obviously the popup is fake, there is no Firewall on iOS, the IP address is wrong, etc.
Is AnchorFree (makers of HotSpot) resorting to scare tactics to push their product?
Is the HiDef Radio app compromised?