The company says anyone who accessed the Japanese-language home page between June 5 and June 14 may have been redirected to a Web site that installed malware on their computers.
Toyota says no sensitive customer data was accessed, and the Japanese site was the only one affected. Still, the company says it doesn't know how the hackers got access, or what the malware did to victim's PCs.
The compromised server was shut down immediately after the breach was discovered on June 14.
According to the Wall Street Journal, Toyota says this is the first time its Web site has ever been hacked.