If you ever download a multi-currency wallet or a wallet that is provided by a 3rd party and not the original developers of the currency, you must know that you are vulnerable.
Many fake wallets have been released, and most of them are on mobile. We will never recommend anyone to use a mobile wallet to hold large funds since their security is easily compromised, but also since a lot of them are fake and just here to steal your funds by making your deposit into the scammer’s wallets, or by taking your private keys.
It is one of the easiest ways to scam people.
Also, be aware of the unofficial forks of coins. Some forks promise you to give you their forked coins if you send them your private keys and then steal your coins.
Not only fake wallets can steal all your coins, but they can also be malware that can access to your private information or even be ransomware that will encrypt all your data and erase them unless you send the hacker a large number of bitcoins.