Ullrich and other researchers at the Internet Storm Center are warning users to not use Telnet anymore -- on any system. "It's archaic at this point," says Ullrich. "Never use Telnet to log in to a system. Use SSH instead. There's just no reason to use Telnet. I don't know why they keep it enabled. They really shouldn't."
Preventing access to telnet would prevent this flaw from being exploited, though many companies still rely on it. You can read the SANS notification on it here.