Users document their infections.
The websites of JB Hi-Fi, one of Australia's largest retailers, and PC hardware forum Overclockers, were compromised over the weekend.
Hundreds of users have been reporting malware infections and other issues from Friday evening, with users posting details of their experience on broadband forum Whirlpool, which ironically faced its own security breach a week earlier.
Overclockers had been hit for the second time in quick succession. The site reported a security breach just over a week ago and is currently offline due to "technical issues". Whirlpool users reported JB Hi-Fi as having a similar issue.
The Whirlpool forums are crammed with users reporting redirects, drive by downloads and even malicious adverts that redirect victims to sites in Asia and Eastern Europe.
"It seems that some of their [JB Hi-Fi] ads have been hijacked and link to some Czech Republic websites which are registered with Norton as hosting harmful material," wrote Whirlpool user rtw.
"Just to let everyone know ... overclcockers.com.au is currently being redirected to malware site leasycrabs.cn," wrote Whirlpool user xconvergex.
Drive-by-download attacks usually prey on unpatched vulnerabilities in users' browsers or operating system. If successfully executed, victims need only visit a compromised site to be infected by malware.
JB-Hi-Fi's spokesman was not available for comment today. Overclockers had not responded to a request for comment.