Wi-Fi the secure internet connection..

Using insecure internet access - such as Wi-Fi in coffee shops, libraries, and so forth - there's a real risk of session hijacking,"When users’ sign on to mail, their login name and password are encrypted as the data passes back and forth using the secure version of HTTP known as HTTPS.

The risk was from hi-tech criminals who snoop on the unencrypted data passing back and forth to steal ID files called "session cookies" generated when these applications start being used.
In Gmail's case, this could mean they might send e-mails in the owner's name, abuse their identity, change a password, or hijack an account.
"It's a frightening prospect,"
The open letter pointed out that Google used HTTPS to protect the data of users of its Health and Voice applications.While Google does make it possible to use HTTPS all the time when signed on to Gmail, Docs, or Calendar the option was so hard to find that few would use it, suggested the letter.
It pointed out that most users retain default options and were likely to be leaving themselves at risk.