Valve says its cooperative zombie shooter Left 4 Dead has sold over 12 million copies to date.

"Telling people a game is great will sell one extra copy. Letting people play the game – Left 4 Dead is a good example – is much better," Valve writer Chet Faliszek said in an interview with VG247 when asked about why the company doesn't talk about its games until they're ready to be shown.

"All of our pre-release stuff is designed to just let people play it. We just let the game speak for itself because the internet has made this thing where, you can’t pull the wool over people’s eyes any more. They’re going to know you’re hyping."

Left 4 Dead 2 recently got Steam Workshop support, allowing modders to share their creations.

[Source: VG247]