The incident follows the successful hacking of the World Anti-Doping Agency (WADA) by the Russian Fancy Bears group, which has gone on to release confidential information about a string of athletes.

The US Anti Doping Agency (USADA) has also been targeted with CCES, the national anti-doping agency for Canada, saying they do not yet know if any sensitive information has been stolen from them.

The attack is part of the "broader campaign against the global anti-doping movement", the organisation said.

"Obviously, we’re concerned about this security breach," a CCES statement said.

"While we know our system was improperly accessed, at this point the experts can’t confirm that any confidential data was stolen from our system. 

"We’ve engaged the expert services of a leading security firm to conduct a complete forensic analysis and to determine the extent of the breach.

"We know this has been a source of frustration and inconvenience for many of the athletes who are part of the Canadian Anti-Doping Programme, for national and multi-sport organisations, our business partners and our staff. 

"We appreciate your patience and hope to have the situation rectified shortly. 

"Interim measures are in place to maintain our core services.

"As Canada’s national anti-doping agency, one of our most important responsibilities is the collection and protection of private information from high performance athletes across dozens of different sports. 

"For the vast majority of these athletes, the personal information we have on file is limited to names, addresses and telephone numbers.

"We are keeping a very close eye on this situation and working closely with cyber security experts and law enforcement officials.

"We’ll be back up and running as soon as it is safe and secure to do so. 

"Rest assured, we won’t take that step until we’ve taken whatever corrective measures may be necessary."

After the hack on WADA, Fancy Bears published information on Therapeutic Use Exemptions (TUEs) permitted to many top athletes, including several Rio 2016 Olympic medallists. 

The hack was seen by many as an attempt to distract from the Russian doping crisis, with TUEs allowed under doping laws to treat medical conditions. 

This means that none of the athletes targeted are thought to have broken any rules, although the hack did spark a debate about the use of substances which are normally on the WADA banned list.

The CCES admitted that it did have the TUE information about some Canadian athletes on file, with no suggestion made that Fancy Bears are involved in the hacking attempt on them.

"CCES maintains information about athlete whereabouts," the statement added.

"And for a small minority of athletes, medical information is collected as part of an application for a Therapeutic Use Exemption, where treatment of an athlete’s condition or illness requires medication that is included on the WADA’s Prohibited List."