How to check if someone has installed Trojan virus on my iPad, received a scam email saying they had

Scam.

See >>> Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

If you are unsure of the source or provenance of a message or alert, do not respond to, or engage with, the message. Certainly do not, under any circumstances, attempt to contact anyone using the contact details that may have been provided within the message itself.

Most scam alerts are designed to scare the unwary into giving away sensitive information - or to fool you into doing something that you shouldn’t - usually to defraud you financially.

There are no Antivirus Products available for iOS/iPadOS. Those that claim to provide AV protection are little more than “snake oil” - and should generally be avoided. Many are simply a vector to install software that will actually try to cause harm to your data, or perpetuate the scam.

Providing that your iPad has been kept up-to-date with system software updates, you should not be overly concerned for your iPad being directly compromised by malware. Due to the system architecture of iOS/iPadOS, unless jailbroken, your iPad is not susceptible to traditional malware infection per-se. However, as with all computer systems, there are still vulnerabilities and exploits to which you remain vulnerable. For older devices, no longer benefiting from regular security updates, the risk of an unpatched vulnerability being exploited increases. Regardless of the installed version of iPadOS, there are useful mitigations that can be used to significantly reduce your exposure to risk.

Threat Mitigation

The majority of threats to which you will be invariably exposed will surface via web pages or embedded links within email or other messaging platforms. Browser-based attacks can be largely and successfully mitigated by installing a good Content and Ad-blocking product. One of the most respected within the Apple App Store - designed for iPad, iPhone and Mac - is 1Blocker for Safari.

https://apps.apple.com/gb/app/1blocker-for-safari/id1365531024

1Blocker is highly configurable - and crucially does not rely upon an external proxy-service of dubious provenance, often utilised by so-called AntiVirus products intended for iOS/iPadOS. Instead, all processing by 1Blocker takes place on your device - and contrary to expectations, Safari will run faster and more efficiently.

Unwanted content is not simply filtered after download (a technique used by basic/inferior products), but instead undesirable embedded content is blocked from download. The 1Blocker product has also recently introduced its new “Firewall” functions - that are explicitly designed to block “trackers”. Being implemented at the network-layer, this additional protection works across all Apps. Recent updates to 1Blocker has introduced additional network extensions, extending protection to other Apps.

A further to improve protection from exploits is to use a security focussed DNS Service in preference to automatic DNS settings. This can either be set on a per-device basis in Settings, or can be set-up on your home Router - and in so doing extends the benefit of this specific protection to other devices on your local network. I suggest using one of the following DNS services - for which IPv4 and IPv6 server addresses are listed:

Quad9 (recommended)

9.9.9.9

149.112.112.112

2620:fe::fe

2620:fe::9

OpenDNS

208.67.222.222

208.67.220.220

2620:119:35::35

2620:119:53::53

Cloudflare

1.1.1.1

1.0.0.1

2606:4700:4700::1111

2606:4700:4700::1001

Use of the above DNS services will help to shield you from “known bad” websites and URLs - and when used alongside 1Blocker, or other reputable Content Blocker, provides defence in depth.

There are advanced techniques to further “harden” iOS/iPadOS (such as using DoH, DoT and DNSSEC). Apple has recently introduced its new Private Relay to its iCloud+ subscribers - in part employing ODoH (a variant of DoH) as an element of this new functionality. If you have subscribed to iCloud+, and have a device capable of running iOS/iPadOS 15.x or later, this feature is included. 

Viruses work by spreading themselves from one application to another. The iPhone and iPad operating systems like to isolate apps from each other. I don't believe that iPadOS would allow an ordinary app to read the files containing other apps' code – much less, modify those.

A "virus-infected" app couldn't spread the virus to other apps. And a "virus scanner" app couldn't read the code of other apps to check whether they were infected. I don't believe there is any way for you to check – and I also don't think there is any need for you to do so. It's a pretty sure bet that your iPad is not infected, and that the message is a total lie.

The scammers who sent the message are hoping that you don't know this – that displaying the scary phrase "Trojan Virus" will be enough to frighten and fool you into believing that you have one.

This is a very common scam message. One, there's no such thing as a Trojan virus. It's one or the other. Two, it's just an email. It could just as well said your hair was currently on fire, and it would be just as truthful.

You only need to do one thing. Delete the email and ignore it.

MileHigh3oh3 wrote:

So not true

While it is very unlikely that your iPad has been infected with malware, there are still vulnerabilities and exploits to which you remain vulnerable.

Be wary of an often repeated myth that Apple devices are immune to malware; those that perpetuate this fallacy, perhaps with good intention, do not comprehend the broader threat landscape. Apple expend considerable resources in developing and issuing regular software security updates and patches for its products; if the myth had any substance, regular security updates would be unnecessary.

If you have not jailbroken your device, that would not be possible.

So not true

What's not true? It is incredibly difficult to directly infect the hardware of an iPad or iPhone. Nearly 100% of such intrusions are hackers getting their user account, not the device.