Also, to the people talking about doing their own backups:
Don't just put it on your HDD or an external drive. Have at least 3 different storage mediums as backups (with at least one being offsite). This basically guarantees that you will never loose your stuff.
HDD + Cloud Storage + Ex...
This wasn't a DDOS, it was a hack. Different things.
Source code does not nessicarally give access to everything. In this case, it didn't.
The Exploit was through ImageMagik, which allowed the code to be obtained, allowing the attacker to search it for vulnerabilities.
Its especially not scary because of Kerchoffs' Principle, which postulates that you should assume that an enemy/hacker/adversary has access to your complete source code/algorithms, and that you should design your security to take account of this.