Is "malfile.exe" a virus? What does "hmtcd.dll" do?

PC users sometimes come upon unfamiliar files on their hard drives, and identifying them is often a challenge.

Many were fooled by a hoax e-mail that circulated a few years ago, instructing them to delete the alleged virus file "jdbgmgr.exe." The file was perfectly innocuous, but it wasn't easy to know that.

Internet security company Bit9 Inc. this week launched fileadvisor.bit9.com, a Web site that attempts to bridge that knowledge gap.

Visitors can search data on 25 million Windows PC files, collected from Microsoft Corp., IBM Corp., the National Institute of Standards and Technology and other sources.

Visitors can search using filenames, but this approach can be fooled by files that appear in several applications under the same name, or viruses masquerading with a legitimate file name.

For more accuracy, users can download a small, free application from FileAdvisor.

When the user right-clicks a file, the application gives the option of computing a unique number that identifies the file. That number is then compared to the FileAdvisor database, giving a better chance of identification.

It may be surprising to find that even with 25 million files in its database, FileAdvisor can come up empty. It identified "malfile.exe" correctly as a file that ships with Windows, but was stumped by "htmcd.dll."