The Personal Computer gaming industry dates back to the 1960s but really began to boom with the release of Wolfenstein 3d and Doom. Nonetheless, in 2005 consumers spent $1.4 billion on video games for PCs in 2005, according to research released by analysts NPD Group. Of that, $344 million came from subscriptions to online games and gaming Web sites, according to NPD's estimate.[1] This number has since increased along with the generally growing video game market and with the release of popular PC games such as World of Warcraft and The Sims. The worldwide PC-based game market is worth as much as $10.7 billion as of 2008. This number includes retail sales, online revenue, digital distribution and relevant ad sales.[2]