Where next after 2nd Line Support?

Left school at 19, managed to get a 6 week contract working for a large company during their roll-out to Win7. They hired me full time after the 6 weeks and since then I have been working in 2nd line support for the last 18 months. They approached me, keen to develop my skills into a more specific area, my question is, in what? I'm interested in InfoSec and also 3rd Line support? What training courses/career paths do you recommend? I'm pretty new to the game.

Thanks in advance.