Pidgin

Pidgin is chat software. It supports the following chat networks: * AIM * Bonjour * Gadu-Gadu * Google Talk * Groupwise * ICQ * IRC * MSN * MySpaceIM * QQ   * SILC * SIMPLE * Sametime * XMPP * Yahoo! * Zephyr

There are also many plugins, like facebook chat, twitter and music tracker. If someone blocks you on MSN, you can see they've blocked you with pidgin. If you use pidgin, you should definitely check out OTR.

Preventing Spam
Tools --> Privacy

"Allow only the users on my buddy list"

Download pidgin