Valve, a company that operates solely online, takes its security pretty seriously and has a good reputation in this area. However, at the time of writing, its Steam forums are down, having suffered a hack attack earlier today. Visit the forums now and you see a message saying "The Steam Forums are temporarily offline for maintenance. Your patience is appreciated." This attack was apparently done by hackers who want to offer free game cheats (but one should be wary of stealthy malware payloads) since before the forums were taken down, they had planted this message:

Ever wanted to dominate the servers you play on with guaranteed results, but you were too afraid to cheat because of ban risks?

The rest of the message then recommends a website where one can obtain all sorts of illegal game cheats, hack tools and porn. Some Steam forum users even received an email with this text, such as this NeoGAF user. There's no indication that any user's account information has been compromised. However, if you haven't yet set up Steam Guard, now is a good time to do so, along with changing your password when the forums come back online. Also, be sure to use different a password for every login. Of course, many other gaming forums have been hacked in the past and just this year saw many hacks against such big names as Nintendo, Sega, BioWare, Epic Games and of course Sony, which was hacked many times over in protest at their business practices, such as removing the OtherOS feature from their PS3 console.