Malicious hackers commonly use a technique called the ‘man-in-the-middle attack’. In that attack, the bad guy interposes himself between two people who are trying to communicate, eavesdrops on their communications, and potentially alters their messages. For example, let’s say Adam is hanging out at a coffee shop when he remembers that he needs to email detailed wire transfer instructions to his new investor, Barbara. If Chuck hacks into the wireless router, he can intercept Adam’s email, insert his own bank account details, and forward the altered email on to Barbara. Since Adam and Barbara don’t know there’s someone monitoring and modifying their communications, they won’t realize they’re being duped until Barbara’s money is in Chuck’s bank account.