Swimming Australia's website has been hit by a denial of service (DoS) attack.

The ABC has learned the site is operating in an "under attack" mode in the wake of Olympic gold medallist Mack Horton's comments about his Chinese competitor Sun Yang being a drug cheat.

While the site has continued to operate, it has deployed software to check the veracity of every browser accessing the page to ensure they are legitimate.

Horton's social media has been bombarded with hundreds of thousands of negative comments from China.

Swimming Australia is not commenting publicly but it is understood the attack has been referred to the Government for investigation.

Security analyst Marco Ostini from AusCERT, a non-profit organisation that protects organisations from cyber attacks, said DoS attempts were extremely common.

"It's actually a very difficult problem to put a number on," he said.

"It's certain though ... based on all malicious metrics on the internet, it's increasing."

Mr Ostini said without seeing the internet traffic and logs associated with Swimming Australia's page it was hard to work out what had happened, but he doubted it was a high-level attack.

"I'd be really surprised if it was [China] state-sanctioned attackers causing trouble for Swimming Australia," he said.

"It's possibly more likely just a large amount of interested people who are expressing themselves in possibly posting comments [on the website]."