Now i am use Myetherwaller, I find it very safe and secure and many people are using it, if i don't share my wallet to anyone, why hackers can steal my coin?
You can get to the phishing site (it's a human factor) or your computer can be hacked.
Currently it is difficult to be hacked because there are many programs that prevent malware. So I see very few cases of hacking and losing all money. Most hacked people have revealed their private keys to the outside
I'd also assume that most people getting their wallet compromised fell victim of phishing-sites but I completely disagree about the claim that it's difficult to be hacked because of antivirus-software.
Antivirus-Software might introduce new vulnerabilities and lead to a (false) feeling of absolute safety but in reality most Antivirus-Software can be easily bypassed by obfuscation (Crypters).
Doesn't mean you shouldn't use Antivirus-Software but keeping your system up to date (Security Updates) and using brain.exe is much more important.