Jakala on "All my wordpress sites have been hacked"

HI,

So at work, we have quite a few wordpress websites- all for different purposes. For some pain-in-the-ass reason, some pathetic little keyboard warrior has sent what i assume to be a virus through our server and all our wordpress sites have been infected and shut down.

However, its only the wordpress sites on the server that have been infected, not any of the others. Therefore, i think the weakness is related to something we have set on wordpress.

Does anyone have any ideas or advice on how we could prevent this from happening in the future?

Thanks!