I’ve had exactly this as well. It took me a while to find this thread but anyway. I was using WP 2.7.1 also when it happened to me. The thing was I didn’t realise what was going on for a very long time. I was getting reports that the WP page was blocked for malicious content, but I didn’t realise the page was just trying to pull from an external ip address until i checked the page source. My site is hosted, and I wrongly assumed that 74.222.134.170 was the ip address of the hosted server. I’d been hit by a major bit of hacking on my website a few months ago, and thought that maybe the warning message was from an old index. Anyway… I can safely say that changing the wp_ prefix won’t help prevent this as mine had already been changed.
Thanks for the tip about the 2 security plugins, I’ve just installed them both.
Google https://74.222.134.170/stats.php?id=2
and it looks like a lot of sites have been hit by this.