I don't use yahoo I have hotmail but I too had the rootkit virus last month. It arrives through the e mail sites. Even after it was removed(@$180.00) it kept trying to re enter but luckily this time my Norton antivirus blocked it. The virus made several attempts to re enter. Luckily it finally gave up on me. (That's probably why it's going after you now
).
Rootkit allows you to continue using your computer but it will make everything slower and slower until it won't run at all. I don't think you will lose any files though. At least I didn't.
Good luck Lee.