Online game publishers including Electronic Arts and Valve have been attacked by cyber hackers, disrupting gameplay.

Reports revealed that game services from both firms have either not been accessible or been slowed due to DDoS attacks, which blocked the gaming websites, the Wall Street Journal reported.

Earlier, hackers also targeted EA city-building and urban planning simulation video game SimCity by modifying game’s code and made it an offline, single-player game.

Valve is all set to launch its Steam Machine gaming console this year, which features a "high-end, high-performance box, built out of off-the-shelf PC parts", it said.

Recently, servers of popular online games including League of Legends (LoL), Dota 2, Club Penguin and Battle had been taken offline by Derp hacking group.

Attacks were mainly aimed at US pro-gamer James Varg, while they also took down other online gaming titles such as Dota 2, Club Penguin and Battle.