Google's acquired VirusTotal, which offers a free service allowing users to scan files and website URLs for malware.
The value of the deal wasn't disclosed, but the company describes itself as 'a small, resource-constrained company'. Founded in 2004, it uses several dozen anti-virus packages to check files and websites for malware.
It offers browser plugins for Chrome, Firefox and Internet Explorer.
Google hasn't said what it plans to do with the acquisition. However, says VirusTotal, "This is great news for you, and bad news for malware generators, because the quality and power of our malware research tools will keep improving, most likely faster; and Google’s infrastructure will ensure that our tools are always ready, right when you need them."
Like many security firms, VirusTotal shares its results with other vendors, and the company's committed to continuing to do this.
"VirusTotal will continue to operate independently, maintaining our partnerships with other antivirus companies and security experts," it says.
"This is an exciting step forward. Google has a long track record working to keep people safe online and we look forward to fighting the good fight together with them."
The chances are that Google plans to integrate the VirusTotal service - and database - into its existing scanning procedure.
"Here’s a little secret. Having a huge index of suspected and confirmed malware is really handy for protecting hundreds of millions of users," writes Google Chrome security engineer Justin Schuh on Twitter.