One of the best features of AIM (at least since 5.2) is that you can have an SSL certificate encrypt your conversation (so long as you and the other party have a valid certificate).
There are a load of "self signed" and "expired" certificates everywhere; today I'm going to walk you through getting a free certificate through a trusted root provider.NOTE: YOU MUST USE IE TO GET THIS CERTIFICATE!
and click "Get your Free Secure Email Certificate now!" (yes, I understand it's an email SSL certificate). Fill in all of the fields requested on the page (Note that First Name and Last Name will be the "Display Name" on the certificate; Myself I have "UGN" and "Security" as my name on my certificate).
You'll recieve a verification email, approve the action and view the site (in IE, firefox will NOT let you automatically install the cert to your computer!).
Minimise all of your windows and right click on the Internet Explorer icon and choose properties. Go to the "Content" tab and click "Certificates". Click on the certificate that you just imported (it'll be the one with the name you entered in on the above form). Click "Export" and then enter the following:
1. Export Private Key
2. Include all certifications in the certificate path
3. Enable Strong Protection
4. Leave "delete certificate" deselected.
5. Enter a password in that'll protect your key, make it something you'll remember as you'll need it later.
6. save the certificate.
Now, open AIM, click "MyAIM" and "Edit Preferances" under the "Edit Options" option. Scroll to "Security" and click "Advanced" and then click "Import", now from the "type" dropdown choose ".pfx" and select the key you exported from above.
At the first password screen just leave the passwords blank, ONLY ENTER A PASSWORD on the first screen if you want to be the only user on your machine to use the key (it gets piss annoying, I leave it blank). Now on the second password screen enter the password that you used when you expored your key from Internet Explorer. Follow the prompts until completed.
Now, close AIM completely and then open it again and enjoy your new certificate. Your friends will be able to see a "lock" next to your name which will show that you're using an SSL certificate. So long as they have a certificate you'll be able to join the user in an encrypted chat on AIM (yeh, we know it's not THAT much, but it's better than nothing yes?).
NOTE: The "Trusted Root" is Comodo.