If you do everything that the author of the topic listed, the only thing that can happen is the hacking of the MEW database itself, but I do not think it's possible at all. Why? Well, if only because if it could be done, it would have been done long ago and more than once and believe me no one would have used MEW anymore.
Agree, if it could be hacked then no one is using it right now. I believe that MEW is safe for hackers because it is widely used by users in the crypto community and the only problem it had when there is phishing site similar to MEW but it can't be considered hacking.