IPv6 problem.... possible attack ??

Hi,

I recently had a weird behaviour on my machines...

Some of may machines, decided to pass to IPV6 !! instead of IPv4 .
I had to reformat 2 Windows machines and one of my Centos server couldn't access the ethernet card.

- Do you think that it could be an Attack ??
- How can I remove completely networks cards and re-install it from scratch ??

i am starting to re-install the complete system, but in the future, I would prefer NOT to do it

Thanks and regards,
.