United States Anti-Doping chief Travis Tygart has condemned as "cowardly and despicable" a cyber-attack in which the personal details of high-profile Olympic athletes were illegally accessed.
Hackers claim to have obtained information relating to the likes of American tennis stars Serena and Venus Williams and four-time 2016 gymnastics gold medallist Simone Biles.
However, Tygart, chief executive officer of the US Anti-Doping Agency (USADA) hit out at what he described as an attempt to "smear" clean athletes.
He said: "It's unthinkable that in the Olympic movement hackers would illegally obtain confidential medical information in an attempt to smear athletes to make it look as if they have done something wrong.
"The athletes haven't. In fact in each of the situations, the athlete has done everything right in adhering to the global rules for obtaining permission to use a needed medication.
"The respective international federations through the proper process granted the permission and it was recognised by the the IOC (International Olympic Committee) and USADA.
"The cyber-bullying of innocent athletes being engaged in by these hackers is cowardly and despicable. It is time for the entire international community to stand up and condemn this cyber-attack on clean sport and athletes' rights."
Cyber espionage group Tsar Team (APT28), which is also known as Fancy Bears, is said to have accessed information concerning substances for which athletes have sought and received therapeutic use exemption.
Speaking about Biles, Steve Penny, president of USA Gymnastics, said: "Simone has filed the proper paperwork per USADA and WADA (World Anti-Doping Agency) requirements and there is no violation. The International Gymnastics Federation, the United States Olympic Committee and USADA have confirmed this.
"Simone and everyone at USA Gymnastics believe in the importance of a level playing field for all athletes."
WADA revealed on Tuesday that hackers had illegally gained access to its anti-doping administration and management system (ADAMS) database via an IOC-created account for the Rio Games.
Director general Olivier Niggli said: "WADA deeply regrets this situation and is very conscious of the threat that it represents to athletes whose confidential information has been divulged through this criminal act."
Niggli revealed that the agency was contacting those athletes involved, and slammed the breach, which he claimed was designed to undermine the organisation's efforts to stamp out the use of performance-enhancing drugs.
He continued: "We are reaching out to stakeholders, such as the IOC, IFs (international federations) and NADOs (national anti-doping organisations), regarding the specific athletes impacted.
"WADA condemns these ongoing cyber-attacks that are being carried out in an attempt to undermine WADA and the global anti-doping system."
The attacks are understood to have originated in Russia in the wake of the McLaren Report, which uncovered a state-sponsored doping programme and led to some competitors being banned from this summer's Olympic Games and the blanket exclusion of the country's athletes at the ongoing Paralympics.
Niggli said: "WADA has been informed by law enforcement authorities that these attacks are originating out of Russia.
"Let it be known that these criminal acts are greatly compromising the effort by the global anti-doping community to re-establish trust in Russia further to the outcomes of the agency's independent McLaren investigation report."
The latest incident followed an attack in August during which the personal details of whistle-blower Yuliya Stepanova, a Russian 800m runner, were illegally obtained.
WADA said it was taking the current situation "very seriously" and was carrying out both internal and external security checks as well as working with law enforcement authorities in a bid to protect ADAMS users.
The Fancy Bears hack team claims on its website that it will show how "tainted" Olympic medals have been won.
It says: "We are going to tell you how Olympic medals are won. We hacked World Anti-Doping Agency databases and we were shocked with what we saw.
"We will start with the US team which has disgraced its name by tainted victories. We will also disclose exclusive information about other national Olympic teams later."