Some of the largest companies in the world, trusts WordPress.
Look at this infographic from Themeisle, it shows some of the most famous. Among them Facebook. Most people will, rightfully, say Facebook is not WordPress. Nope, you are right, Facebook is not. But The Facebook newsroom is. Microsoft, they have C# and ASP.NET why would they use WordPress? Probably because it is fast to install, easy to change, and very easy to use and maintain, even if you are not an expert computer user. Microsoft uses WordPress for the newsroom too.
That is why we also use WordPress, and recommend our customers to do the same. WordPress is updated very frequently, that is the biggest plus in using an open source system, a lot of programmers all over the world are looking for errors and weaknesses. And corrections are spawned very often.
WordPress has a very stron build in security system, but as standard in a new webpage, we do install additional security plugins.