A company source said the company is "almost 100 percent sure" the attack exploited a flaw in its Kayako security appliances which allowed the attacker to spam its users.
According to the source, the hacker blindly injected the HTML spam into the support system but was denied access to client information.
Servers Australia Manager Jared Hirst reassured the company's customers in an e-mail response, that their personal data was not compromised and warned against following the links provided in the e-mails.
"I am writing to let you know that someone injected spam e-mail into our support system and managed to send it to all of our customers," Hirst said.
"They have not gained access to any e-mail addresses or personal information because they injected the spam into our system.