Just use forum search option with keywords "electrum, stolen, hacked" and you'll find dozens of threads by users who have become victims in one way or another. This was especially pronounced when someone took advantage of a vulnerability in Electrum itself and displayed a false message, which deceived many to download fake Electrum.
Electrum is safe to the extent that we use it wisely and correctly. Even if we follow the safety instructions, verify the signature and install Electrum the responsibility must not stop at that step. Making sure that the device on which we use Electrum is virus/malware free, and that the backup is properly secured is also a part that should not be neglected.
Nonetheless, I think most will agree that Electrum as a hot wallet is not for storing large sums. If someone has a $1000 + worth of BTC, then I guess they can pay a few tens of dollars for a higher level of security (hardware wallet).