It is important to make sure that your computer is capable of generating random numbers. In 2013, for example
a flaw in Android devices prevented them from generating cryptographically random numbers, which resulted in the risk of malicious actors being able to steal any coin stored on Android devices. The above did not ever affect electrum.
But how would people know their
computer OS is capable of generating
secure random number? Most people simply assume the OS is secure and some of them only know about it after such vulnerability is disclosed.
I was hinting at things such as malware that would prevent the OS from generating a secure random number.
Today, most computers and mobile devices can generate cryptographically random numbers. However, if your device is infected with malware, the malware may cause your computer to generate numbers in a predictable manner, which could lead to a hacker stealing your money, even if you generated the seed on an offline computer (that was infected with malware).
While it's possible, it's not practical when the malware could simply copy wallet file, steal password using keylogger or read private key from RAM when the wallet opened by user. Are there any known malware which specifically mess with system cryptographic secure PRNG?
If the malware is targeting users who are going to be generating private keys on offline computers that will never touch the internet in the future, stealing information is not going to do very much because it would have no way of transmitting the stolen information.
My guess is that any malware that targets PRNG is going to be state-sponsored whose targets are embassy employees and spies, so their communications can be intercepted and decrypted.