This is definitely not the right forum because (a) it has nothing to do with backtrack and (b) its not even close to an expert topic... but I'm in a helpful mood, and bored, so I'll offer my thoughts. First off prevent future attacks by changing all your passwords, and make sure your system is secure. Info on your operating system(Ubuntu? version?), connection type(wireless?), and services running(file sharing, remote desktop?) would help me suggest security measures to implement. I can't think of any connection between a ddos(which it seems you're suggesting, but connections from all over the world are more likely do to file sharing in my opinion) and a system compromise. The fact that spam was sent from your account(I'm assuming) to all your contacts sounds like come sort of malware to me since an individual attacking your system would have little to gain by spamming your buddies. Send me a private message containing your IP address if you would like me to do a quick scan to see if you have any obvious vulnerabilities. Or better yet, download Backtrack and attempt the scan yourself if you have confidence in your linux skills.