Go Update W3 Total Cache, WPTouch, and AddThis RIGHT NOW!
If you’ve updated your plugins in the last 24 hours, go straight back into your website and do it again – there’s a chance you may have downloaded some infected plugins that were hacked into the repository.
According to WordPress.org, the plugins AddThis, W3 Total Cache, and WPTouch were infected with a backdoor that lets people into your site. The plugins are fixed now, and if you update you can remove the infected code immediately.
Normally those plugins are safe, and (given the hacks and the frequent downtime by other companies) it’s nice to see a company like WordPress that can think on its heels and get the hacks solved in minutes (and not weeks – I’m looking at you Sony).