"And one more thing, I don't recall that Informix, DB2 or Oracle have had viruses released targeting them. But of course, that will never happen again with MSSQL..."
To be fair, if theres a web server into it, you can use sql injection on just about any informix or oracle database. In fact, in my experience (and I am an informix fan) our ifx developers are kind of lazy about writing with stuff like this in mind because they all assume that no one targets informix. The old security via obscurity mindset - total b.s. I know.
Also, theres entire websites devoted to hacking oracle - its not that nobody does it, but istead that you find such software in high dollar installations and not every 13 year old in the world has access to such big iron.