loopback 127.0.0.1?

I'm trying to get some correct advice on this loopback ip address 127.0.0.1, what exactly is this? and y is this now on my new MBP, as well as my iPhone4? The only way i was able to discover this was a network scanning program on my comp. I also found it on my iphone4 later on with a network scanning type app. I have reasons to believe that this is malicious but i don't know for sure. I would appreciate any kind of help with this. Thankyou

127.0.0.1 is the local address for all network devices - it is a way for machines to test they have layer 3 networking ability (the ability to connect to IP addresses (these are used on your internal network (between your router and iphone, imac, etc) and they are the numbers that the domain names (like mac-forums.com) map to - basically if you want your computer to talk to anything else, anywhere, then you want it to understand layer 3 addresses).

I've simplified it a little here, but ultimately - it is good that you have a local address (or loop-back address), all computers with network ability have one and it is nothing malicious.

More info if you want it:

OSI Model (explain what I mean by layer 3)

Wiki: Localhost address

Relax, all is well

NOTE: you may also see an entry such as ::1 in hosts files. This is essentially the IPv6 equivalent of 127.0.0.1. Some systems will have issues on IPv6-aware networks if this entry is not present, though not all systems on all networks.