Is Tetris "copyrighted"?

Odds writes "I wrote a shareware Tetris game five years ago. I got an e-mail today from another Tetris author, who received a menacing e-mail from some company called Blue Planet Software. These guys have some deal with Alexey Pajitnov, and claim to have a "copyright" on the Tetris concept. There's a lot of FUD on their web site, talking about "cutthroat pirates" making knockoff games. Now, I'm no legal expert, but last I checked copyright didn't protect ideas. Is this another case of clobbering the little programmers? "