WARNING: The Electrum Bitcoin Wallet has been compromised! Fix has been issued today!
The famous and widely used Electrum Bitcoin wallet is susceptible to JavaScript attacks. All versions except the new 3.0.5 are affected. See this BitcoinTalk announcment, this official tweet, and this github issue.
If you had opened Electrum in the past in combination with an open web browser, your security and Bitcoin are at risk.
If you did not set an Electrum passphrase for your wallet, you should upgrade Electrum immediately, and move your Bitcoin to a new wallet!
If you do have a passphrase protection, you should also upgrade, but your funds may still be secure. In this case an attacker could only get address and transaction information from your wallet and change your Electrum settings.
You can download the new and fixed version 3.0.5 here (verify your download before installing!). Please, share this info and help prevent BTC theft!