What can someone with a sniffer actually see...?

Question

If someone has a sniffer and is pulling in packets, what can they actually see. can they read all e-mails, pages visited, IM's, etc.
yes, I know about securing the network, just want to know what info they can get.

Answer 1

Yes.

Packets have data sections which contain information in plain text. Most packets traverse the network this way. This includes email, web traffic, ftp traffic, etc... If the packets are sniffed, they can be reassembled and the information can be extracted.

The only packets that are not sent in plain text are those that are encrypted. The most common encryption on the web is SSL over HTTP or HTTPS. You have used this probably without knowing. When you visit your bank online, look for a key in the lower right corner of the internet explorer screen. That is an indication of a secure connection.

Answer 2

A sniffer allows you to see all the data your network card is sending out. That does include e-mails, browser messages and even encrypted data. Now with the encrypted data you will just see encrypted data which unless you find a way to decrypt, it won't mean much to you.

Answer 3

Never heard of a sniffer. Is that like spyware?

Answer 4

yep, they can see all of that stuff. anything that goes out of you computer can be sniffed. however, any encrypted protocals can't be sniffed (unless they are doing a man-in-the-middle attack, which you would probably notice because of a certificate error, unless they managed to plant their own root certificate on your computer)