You'll want to update your skills.
C++ is good, but you'll find that the primary language for Unix and Linux system software (kernel, utilities, major applications like GIT, GIMP, most of GNU, etc.) is C. Linus Torvalds (the original developer of the Linux kernel) has one of the more extreme views on the two languages, fwiw:
http://harmful.cat-v.org/software/c++/linus
VB6 is nearly dead. I'm sure there are a lot of legacy applications still running, but the compilers and runtime libraries are all ancient. VB.NET has been the replacement for 15 years or so...but if you want to learn a .NET language then I suggest that C# is the only language designed from the ground up for .NET programming.
HTML has had a major upgrade in HTML5, and JavaScript has been both improved and cleaned up a bit since 2004.
Delphi is still good. No support for Linux or Unix, though. Windows and OSX only for development, with the ability to create apps for Android and iOS.
MySQL is still around and developed by Oracle, but a lot of the open-source community (including many original MySQL developers) have moved to the compatible but "more free" MariaDB.
Projects are important. I'm convinced that you really only learn coding by doing a lot of it. At first, these will be tutorial driven as you learn or relearn, but I think it's very important to strike out on your own. Find something that's a bit harder than you know how to do, and try to come as close as you can to getting that idea working. As you study, write small programs on your own to use the new things you learn.
Security is its own special world, concerned as much with breaking programs as creating them. Good low-level skills are mandatory, or nearly so. One good source to get started with programming specifically for Linux, rather than through layers of cross-platform APIs, is _Beginning Linux Programming_, by Matthews & Stones. It's not a beginning programming book, but rather a book for programmers beginning to learn Linux. For about $30, street price, it's more than worth it.