Can someone use my IP address?

[Alyssa]

I recently found out that the oldest daughter of my mother's boyfriend is being harassed via social networking sites. She took her computer to a computer specialist and he or she traced the IP address AND my Twitter account. I am the only one with access to my laptop but, even if I had a reason to harass this woman, I wouldn't, so how is it possible that everything came back to my IP address and Twitter?
I've only said what was told to me. My mom texted me and accused me of harassing her boyfriend's oldest daughter via social networking sites.

She told me that the daughter took her computer to a specialist who traced all of the messages back to my IP address.

[Ann sers]

Nobody with the proper technical background to honestly this question for you will even be able to understand what you're saying... any other answers you'll get will be meaningless blabber.

"computer specialist" - what does that even mean? Most computer repair people don't even have a college degree.. you can train a monkey to assemble or replace parts in computers... Unless the so called "computer specialist" was a forensic examiner then this is meaningless..and that kind of work would has cost much more money than the computer itself is worth.

"traced the IP address" - what IP address? how did they "trace" it? What does this even mean?

"I am the only one with access to my laptop" - what does that have to do with an IP address? Unless you're home network (assuming you have one) is configured in a certain way then any and all computers connected will be sharing the same IP address... so what does your laptop have to do with anything? and also, you're pretty much implying that you have a static IP address...which is pretty unlikely.

"how is it possible that everything came back to my IP" - how is WHAT possible? and WHAT is it that "came back" to "your IP?"

The most likely scenario I can think of is that someone(probably a friend or family member) guessed your twitter password and used your account to send harassing messaged to someone else... etc..

To answer the question "can someone use my IP address?" - well first of all, what makes you think it's YOUR IP address? IP addresses are not people. Most consumer ISPs in this country assign DYNAMIC IPs.. Also, everyone who is connected to the network at your home (assuming you have one) will be sharing the same IP... and to answer even further, yes, such a thing as IP spoofing or even maliciously hacking your machine and using it as a proxy is very possible.. thought I don't think that's what's going on here.

Honestly, questions like this should be flagged for spam and I already regret typing this response.