It can be used for 100 years... I want know myself how private keys transfered? Do they transfered in ecnrypted format? Do no one can intercept while private keys sending to servers?
as i told you, if you want to know yourself you need to know programming (python for the most part) and go through the code.
here is the link:
https://github.com/spesmilo/electrumotherwise i am afraid there is no other way, other than trusting other people's judgement.
of course you can always ask/pay someone whom you know around you to go through the code and check it for you.
It give - transfer keys to the servers, because this is the only way to connect to the blockchain and receive your bitcoins.
this is the only way that "you can think of" as i said above you should read more about basics of how bitcoin works.