今天尝试通过 安装包apt-get，但是遇到了很多404错误。sources.list上周五我正在全力工作（我的知识没有变化），现在我得到：
W: Failed to fetch http://ftp.fi.debian.org/debian/dists/lenny/main/binary-amd64/Packages 404 Not Found [IP: 130.230.54.99 80]
W: Failed to fetch http://ftp.fi.debian.org/debian/dists/lenny/main/source/Sources 404 Not Found [IP: 130.230.54.99 80]
W: Failed to fetch http://security.debian.org/dists/lenny/updates/main/binary-amd64/Packages 404 Not Found [IP: 212.211.132.32 80]
W: Failed to fetch http://security.debian.org/dists/lenny/updates/main/source/Sources 404 Not Found [IP: 212.211.132.32 80]
例如，当我浏览http://security.debian.org/dists/ 时，似乎没有 lenny 目录。有什么问题？