Undo-ing change of genre - hardest question ever!!

Question

I accidentally changed the genre of all of the songs in my library (4000 plus songs) to Hip-Hop. Is there anyway to undo this? Or to get songs to revert to the genre they were originally listed under? I really like listening to songs sorted by genre (and obviously don't want to have to manually correct the genre's of over 4000 songs).
Thanks so much for any help you can offer.

Answer 1

Don't right click and Get Info.
Go to the menu Advanced -> Get CD track names.
This looks the info up on the Gracenote CDDB (where iTunes got the names in the first place).
http://docs.info.apple.com/article.html?artnum=304297
"Get Information for CDs from Offline Imports
If you're connected to the Internet, iTunes will automatically retrieve information about any CD you play or import with iTunes, including the name of the artist, album, and each song on the CD. If you're not connected to the Internet, you'll notice that all the songs you import will have generic names such as "Track 1," "Track 2," and so on. Once you connect to the Internet, you can replace them with the actual CD information—just select the songs and from the Advanced menu, choose Get CD Track Names. iTunes will retrieve the names of your selected songs and apply them automatically, even if the CD is no longer in your computer."