Valve’s digital games distribution service Steam suffered a worldwide failure for several hours on Sunday, leaving users unable to play games as well as taking offline the Steam user forum and various associated websites.

Despite claims from concerned users suggesting the popular gaming platform could once again be under attack, the fault was eventually traced to a failure of their central datacenters uninterruptable power supply (UPS) system. "Our data centre's uninterruptable power supplies experienced a power failure", an engineer posted on Steam’s forum yesterday. "The power is back on now and we're working to get service restored as quickly as possible."

A UPS system is a battery backup solution that is used to provide power when mains electricity fails, keeping servers running during brownouts and other intermittent power supply problems, while providing enough time to shut them down in the case of prolonged mains failures. In larger datacenters they're often supplemented with diesel generators which can be used to provide power during extended periods of power loss. UPS systems are situated between the power grid and the servers and when faults occur they often disrupt power to devices attached to them even if the mains supply is unaffected.

Around two hours later another Valve employee posted saying, "we are up and running at a normal user load. There are a couple of lingering issues which we will continue to work on until they are sorted." He also thanked everyone for their patience during the unexpected outage.

On Friday Valve co-founder Gabe Newell contacted users notifying them that the attacks last year were worse than first expected, and evidence has been found that the hackers had stole a backup file containing financial transactions between 2004 and 2008. No passwords were stored in the file and all of the personal information was encrypted. Nevertheless, he recommends users keep a close eye on credit card statements and use Steam Guard to provide an additional layer of protection as a precautionary measure.