The attacks were attributed to Turkish hacker group NetDevilz.
The attack was particularly embarrassing for ICANN as it came just days after the group approved a plan to open new domains for registration by the public.
According to ICANN, the hackers pulled off the attack by infiltrating systems run by ICANN's registrar. The hackers compromised the DNS servers and redirected requests for two of the group's domains.
The company noted that the attacks were only directed towards mirror sites, and that the main .org site was never compromised or altered in any way.
"It would appear the attack was sophisticated, combining both social and technological techniques, but was also limited and focused,” ICANN said in a statement. "The redirect was noticed and corrected within 20 minutes; however it may have taken anywhere up to 48 hours for the redirect to be entirely removed from the internet."
Later, a separate group of attackers used what ICANN described as an "automated attack" to exploit a vulnerability in blogging software WordPress and compromise the site's blog. ICANN does not believe that the two incidents were related.
ICANN said that it will launch an internal investigation on both attacks in order to determine possible safeguards in the future.