grub2 - GRUB disappeared after recent Ubuntu 12/Win7 install?

I recently installed Win7 and Ubuntu 12 on a new build.

Installed windows first, as recommended, and then Ubuntu on the remaining unused drive space.

Everything was working fine, grub allowed me to dual boot properly. Until this morning - switched the machine on, and it booted into windows - no grub.

I'm wondering if a recent windows update may have overwritten the MBR?

So..

• What's most likely to have caused this?


• How do I get grub back?


• How do I stop it happening again in the future?

Thanks!