Is Movable Type among the most secure blogging platforms? I doubt it.
NIST's National Vulnerabilities Database shows the following number of vulnerabilities for WP versus MT between 2009 and 2012:
year MT WP
2009 10 3
2010 5 0
2011 2 1
2012 1 0
Though, to be fair, Secunia shows a very different picture:
year MT WP
2010 3+ 3
2011 3++ 5++
2012 0 1
(Each plus mark(+) represents 1 moderately critical vulnerability. All others are rated as "not critical" or "minimally critical".)
Now, I included the 2009 data from NVD because you mentioned the state of things in 2007. But really anything prior to 2010 is irrelevant since that's when the current major version of each CMS was released. In 2007 people were still using WordPress 2.2/2.3, which is about 9-10 releases ago. And WP3 is also a much better CMS than WP2.
The data I was able to find tells me that, currently, Movable Type is only marginally more secure than WordPress if at all. NVD depicts WP as being far more secure, whereas Secunia tells a much different story, with WordPress having 33% more reported vulnerabilities (though WordPress only has 2 moderately critical vulnerabilities to Movable Type's 3) and 1 unpatched non-critical vulnerability to Movable Type's 0 unpatched vulnerabilities.
That said, WordPress is much, much more popular than Movable Type. As a result, there are far more hackers and script kiddies targeting WordPress sites than Movable Type. And while this is a form of security through obscurity, it does have a practical effect in real-life.
Of course, there are also more whitehat hackers and developers scrutinizing WP's code and trying to seek out and patch vulnerabilities before blackhats can get a chance to exploit them, so if you keep your software up to date, there shouldn't be any appreciable difference between running WP and MT.
Another option, especially for the less technical-minded (or techies who'd rather keep their hands free for other things), is to go with a hosted SaaS solution. Squarespace, Wordpress.com, Blogger, and similar hosted CMS providers will not only free you from having to worry about patching your software, but, at least the paid ones, have SLA agreements that ensure that, even if something were to happen, you'd be taken care of. Plus, the security through obscurity element is much more significant with services like Squarespace compared to Movable Type.