Can my computer be identified by another user if they look up my ethernet address? What exactly is a ethernet address is it like the IP address where every computer has a different IP? my friend said it was like a IP address and I wasnt sure so i came here to ask :) (hope this is the right section)

It is the hardware address of the Ethernet card, typically called a MAC (Media Access Control) address. This value is stored in your OS configuration. You can actually configure a different MAC address and no one care. To your original question, yes, your MAC address does indentify your specific ethernet card (in 99% of cases, these are completely unique). It also is similar to your IP. Both should be unique in a LAN. But your Ethernet address is not sent everywhere. It is only used on your local network segment (LAN, maybe WAN but no further). A MAC address only applies to the physical media you are using to network. Once that media translates to another (say, ATM), the MAC address has little/no context or usefulness. IP is software (virtual) labeling and MAC is hardware labeling.

To add on to what proxy said.... A MAC address is a unique 48bit hex number burned in the ROM of any networking device, NIC, Router, switch, etc. The first 24bits of that MAC address is the manufacturer ID so any products you buy from say linksys will all have the same first 24bits in thier MAC. MAC addresses reside in layer 2 of the OSI model (data-link). These addresses are unique, however you can "spoof" a MAC address quite easily with the right software. To further answer your question. YES, your computer can be identified by its MAC address because any packets leaving your NIC contain a source and a destination address. So every peice of information you send has your MAC stamped on it. Anyone with a packetsniffer can listen to traffic leaving your network and open it up to read the contents (unless encrypted) of that packet and see where it came from where its going and whats being sent. Did you know that emails are all sent in plain text? Along with most Instant Messaging programs. Hell your password to authenticate against your POP3 server is even sent in plain-text (unless your ISP enabled some type of secure authentication method). Makes you feel real secure now doesn't it! :D

>> Did you know that emails are all sent in plain text? Along with most Instant Messaging programs. << Sadly, this is very true. However Zone Labs, the makers of Zone Alarm, do an IM secure application that encrypts IM Messages. Of course both ends must be running IM Secure. Claims to work with all popular IM clients. It does work very well with AIM. Stuart

First, Ethernet MAC addresses do not travel end-to-end across the Internet. That physical layer only operates in local networks and at best between networks. Routers remove MAC addresses from headers and replace them with the destination MAC addresses for the next router. Routing tables have local and next-hop (when on the same medium) MAC addresses, so you would need to see the arp cache of a local subnet router to get the MAC address. By RFC 1433, routers do not forward ARP requests (which translate IP addresses to MAC addresses) not directed at themselves (under 3.3 Forwarding ARP Requests - "If the Target IP address is not the host's address, the host silently discards the ARP Request."). ARP requests work between routers and within subnets. They do not work generally across the Internet for all hosts. Routers can be configured to allow this however. In Windows, the command arp -a shows your local arp cache. Notice, it only includes those MAC addresses on your subnet. The Internet is made up of various networks, some of which carry Ethernet frames. Ethernet frames carry your MAC address. Traditionally, Ethernet was largely a LAN protocol. In more recent developements, it has been extended to include some WAN areas and major LAN backbones (due to its throughput possibilities and new media). While most major telecommunication networks are packet switched (and IPv6, in some cases), they do not operate in Ethernet. Rather, they glue Ethernet networks together. For example ADSL operates (usually) through an ATM network past the DSLAM. ATM networks use MAC addresses, but not Ethernet MAC addresses. When you emulate Ethernet over ATM, you translate between the two physical addresses. ATM tunneling Ethernet will operate more conventionally. Ethernet MAC addresses identifying end-nodes rarely carry over WAN lines. In some places like Japan you can find ISP's which offer Ethernet end-user services. Obviously, the shorter distance between carriers and customers makes Ethernet far more feasible in densely populated regions. There are ways to get remote MAC addresses, but this depends on the setup of the router and clients of the target subnet. In general, it is not possible, but specific situations may allow it. To get a remote MAC address, you can try seeing if a local machine in the traget subnet has SNMP open (poorly configured), is running NETBIOS, has a wake-on-LAN configuration, or has a router specially configured. ARP explanation.