First of all, this is just really annoying and serves no practical purpose, but it's fun.
You can use another packet editor, or messenger, but this guide is for WPE pro with yahoo. It should work similarly.
1. Sign in to yahoo messenger. Make sure it's up to date.
2. Download
WPE pro
3. Add yourself to your friends list.
4. Open WPE pro and click on target program. Then click Yahoo messenger.exe
5. Click the play button in WPE pro.
6. Click the "appear invisible to everyone" option In yahoo messenger
7. Then click the "Available " option.
8. Click the stop option in WPE pro.
9. You should see a window of stuff that you don't understand show up. Don't worry we'll get what we want.
NOTE: If a packet is saying in the destination field "Your IP" THEN DO NOT SEND IT! IT WILL FUCK UP YAHOO AND CRASH!
10. Click the available button again.
11. Right click on the first packet and click on send. If it says in the bottom right that you signed off, look at the number in the open sock ID field, and remember it. If you get this, then right click on that same packet and click on add to send list. If you don't get this, then try the next packet.
12. Now make sure it has you has invisible. Try a packet until it says that you signed back on in the bottom right. When you get this, right click on that packet and click on add to send list.
13. In the bottom left of WPE pro click on send, next to filters. Put a check mark next to each one labeled New Send. Click on the small play button. A menu should pop up. In the timer field, set it down to 100. In the open socket ID place, put that same number you memorized from before.Put a dot next to the continuous option. Press play.

Eventually, it will start to glitch and will separate from the bottom.
Notes: Since you don't edit any information, I think you're safe.
This SHOULD work with Msn. You can remove yourself from your friends list now.
To Kyo: I was going to use your photo host, but it doesn't allow BMP images.
I found this out myself, but it was inspired by my hacker friends.
Have fun! +rep?