Cybercriminals have attacked a website belonging to Moscow-based security firm Kaspersky Lab.
The firm has admitted that its main anti-virus sales website was compromised in an attack at the weekend, after initially denying the attack.
For three-and-a-half hours, visitors to the site were redirected to a fake anti-virus site containing links to malware, according to Australian reports.
"Currently the server is secure and fully back online, and Kaspersky products are available for download," the firm said.
The breach was made by exploiting a third-party application used for site administration, according to a blog post by Rik Ferguson, senior security advisor at rival firm Trend Micro.
"Security vendors have often been the target of both malicious and mischievous hackers and without fail, honesty and transparency have always been the best policy in the aftermath of such an event," he said.