A fishing malware scheme has been spotted targeting electrum wallet users. Electrum users are advised to read the warning explainer that has been setup here.
Users of many versions of Electrum released may see messages as pictured when attempting to send a transaction with their wallet. The message, or some variation of, purports that a security update is required to continue.
This is not the case.
The message is generated by the server you are connected to, and contains a link to a malicious modification of the wallet which, if installed, will result in the immediate theft of all of your money. If you install any software shown in a message such as this you have no recourse to recover your funds.