Bitmob reports that Sony's PSN servers were running the most recent version of the Apache server software when they were hit, countering testimony made to the US Congress claiming that the PSN was running "very old versions of Apache software that were unpatched and had no firewall installed." That testimony was admittedly based on second-hand information.
Using Google's webcache, a member of the Beyond3D forums showed that as of March 23, Sony was running version 2.2.17, which was the latest stable version. If you're so inclined, you can double-check the process of B3D's "deathindustrial."
Outdated servers or not, Sony has PSN, SOE and non-PSN related security issues to work out before returning to reality (and compromised trust) at the end of this month.