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if it applies to mobile phones it will be very easy when newly installed applications will of course require approval for some access on the smartphone.
applications downloaded from official sites may have very little risk. but on a PC or other device, we often download and install applications provided by other developers.
There are some stuff that can easily bypass through a phone's security and even on the app store that are supposedly safe for you to download on stuff, you can see some apps that can bypass through that are Trojan. You also can never be sure of official sites because there are scammers that imitates the official website and pays top dollar to get on top of the search engine results which buries the official site on 3rd or 4th place in the results. The best thing to do is to double or triple check so you are sure that something isn't fishy.
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If a virus has been detected, reinstalling your device is the most appropriate choice to clean everything. As OP experienced, it's possible that the antivirus really didn't detect the virus until we realized when it was connected to a crypto wallet. and the situation is just waiting for us to be careless.
Nope, reformat is the best thing to do if there's a potential that you've downloaded a virus together with an app, that's the only way to remove the virus and be sure that reuse of the computer is clean slate. Virus don't go away just because you've deleted the file that it came with because some of them install themselves somewhere that's different from the destination of the file that they've been with.