Unfortunately many people do not change the default router password because they do not even know about it, or simply do not care. It never crosses their mind that a malicious user can gain access to that interface. Opening a legitimate looking email on an iPhone, iPad or Mac while using an Asus router with a default or guessable password could compromise the security of your internal network.
Read more here – http://www.acunetix.com/blog/web-security-zone/the-email-that-hacks-you/