a public "encrypted" wifi network is no more secure then a public "unencrypted" wifi network. so the answer should be your internet connection is only secure as long as no one else has your wifi passphrase ( password ). anyone with the wifi key can browse your activities just like if you had no encryption at all.
how WPA pre shared key works
each device is given a 8 way handshake packet.
your wifi password is hashed into this handshake packet. the hash consists of your network name and password
and a mathematical formula.
this packet tells the wifi router you are authorized to encrypt and decrypt wifi trafffic.
the wifi router tells each client what the current group key is.
the group key is used to encrypt and decrypt network traffic for all clients.
the group key changes every hour.
authorized clients get the new group key
this is called "rolling keys"
if i disconnect and monitor the wifi traffic, i have to reconnect when the group key changes or i am locked out. some routers can be set to change the group key every 5 minutes. but most are configured to change the group key once an hour
if i am authorized to decrypt network traffic i can easily decrypt yours , because you are using the same group key
how safe is the group key?
very, the group key uses AES-256 based encryption. its very secure unless of course you know the key. the basic rule of thumb i heard was that if you change your group key every hour on the hour, you have to wait at least 100 years for the same key to be used twice.
how do i stop this?
don't give away your wifi password, don't connect to people's encrypted wifi networks you don't trust
whats different about wifi enterprise??
each client encrypts their traffic individually using a different key then anyone elses. no ones key is the same as anyone else key. this is more secure then WPA pre shared key.
don't accept rubber stamp answers that say just because a WPA2 AES network is encrypted means its safer then one with no encryption at all.