The sehllshock bug is a vulnerability in the bash program inside Linus servers. Bash is a comand line interface that allows you to run programs and instructions by comand line only. Its like Command in Windows, but for servers. That vulnerability has existed for a long time, but they discovered it just now. Tom Scott explains what it is and what it does.
Ask your hosting provider if they ran the patches so that you won’t see your sites deleted or otherwise compomised.
Stay safe, guys!