This was a known serious vulnerability in electrum which was warned well before by developers and users on git. Since electrum is a SPV wallet, it relies on other trusted electrum servers while broadcasting transactions. If your transaction is notified by a malicious server run by a hacker it would display a false message to download a new wallet. Upgrading to newer versions of electrum will limit the displaying of such phishing messages but they would be displayed anyway. Anyway versions older than 3.3.3 are more vulnerable to such attacks and would have a high possibility of getting such messages.

Info from git : https://github.com/spesmilo/electrum/issues/4968

If you are a regular cryptocurrency user, you need to keep track of what is happening around you in the technical stuff. Failing that, you will lose your money. Note that, there are electrum forks for Dash and other small coins. Those forked wallet should also be affected. Also if you have downloaded a new upgrade, kindly verify the PGP key of ThomasV to check for original versions of electrum.