Hackers can only get a private key by creating a phishing site that masquerades the original site and entices people to fill it. Or maybe your computer has been infected with viruses and malware, resulting in the private key being stolen. To be safe, you should bookmark the e-wallet website of MEW, then when you need to trade, just click on the bookmark instead of access from the strange links, and should buy anti-virus software to prevent stealing personal information.