Actually not all.
One site was found to utilize “bots” or software that emulated human opponents to play but with the possible knowledge of the cards of the players even when the cards are not yet dealt.
The site was then forced to shut down. Many people who play online poker at the site were surprised at losing every penny they bet on the site.
Since then, several bodies giving out online gaming certifications such as Kahnawake Gaming Commission, and also big auditing firms like Pricewaterhouse Coopers have been evaluating and reviewing online poker sites and getting reviews or feed backs from people who play online poker to improve their standards for certifications.