Several Sites Infected With Malware 2.7.1

In the last day, about a dozen my WP sites hosted on the same IP have been infected with a malware script. These sites are now blocked on FireFox and have been tagged by Google as installing malicious software without the user’s consent. I’ve contacted my host and they tell me they are going to clean it up. I was using very strong passwords. My host tells me that the sites were hacked by someone exploiting a vulnerability in WP 2.7.1.

Now I’m going to have to go to war with Google once the sites are cleaned which I would prefer to avoid. Obviously I’m losing money, big time.

I’m a realy dummy when it comes to this stuff. How can I prevent this on my sites hosted on other IPs?