Even if you have firewalls and up-to-date anti-virus and anti-spyware programs installed on a PC, there are other ways for your personal information to make it into the wrong hands.
"Applications leave traces of information behind. That information can be telling of certain things," said Mike Irwin, chief operating officer for Webroot Software Inc. in Boulder, Colo. "For people that know where to look, it provides a distinct visibility into specific aspects of computer usage by the user."
In addition to developing several anti-spyware programs for general consumers, Webroot also has produced "Window Washer" a software tool that cleans up, or "scrubs" away, fragments of files left behind on hard drives, aiming to protect a user's online privacy.
Webroot debuted version 6.5 of Window Washer this month, and computer security heavyweights Symantec and McAfee have similar tools.
The products address an increasing identity-theft concern.
The most common way that old files are used nefariously is when people donate their old computers or have their machines stolen.
Even if you delete files and empty the computer's recycle bin, they're still retrievable, said Nathan Ziehnert, deputy of counterintelligence for a Denver Geek Squad.
He said that software such as Webroot's is helpful because it permanently and securely deletes files and their remnants from a PC.
"An all-in-one utility makes it easy to do in one step," he said. "Unless you securely delete files, there's no telling what could be on the hard drive. It's something I'd be concerned with if I was ever donating my computer."
Microsoft's Web browsers offer quick ways for people to clear out old Web files and cookies, the small files that Web sites place on your computer to track usage.
"I wouldn't say there's not a need [for programs like Window Washer]," said Paul Cooke, strategic security adviser for Microsoft. "We're seeing people steal more things in real time."
He pointed to spyware that watches user's real-time online activity and can monitor keystrokes of users, capturing passwords and other information. He said Microsoft's newest operating system, Windows Vista, has additional tools to help users clean up their hard drives.
But Webroot counters that its additional utility software is needed because "every application you are using on a PC is leaving many trails about what documents, content and other information has been accessed and viewed," said Gerhard Eschelbeck, the company's chief technology officer.
"Media players, word-processing apps, spreadsheet apps, or even document viewers such as Adobe PDF viewers keep records of the most recently accessed or opened files and documents. This information gives away various clues about the usage pattern on a computer," he said.
However, Webroot and Microsoft officials agree that a person's level of Internet use and what kinds of sites one frequents should determine how often users should "scrub" their hard drives, regardless of the kind of software used.
Downloading files from unknown sources or using "underground" peer-to-peer file-sharing networks puts users at a greater risk of having their online privacy compromised, Cooke said.
"The more risky the behavior, the more often you should clear [your browser and hard drive]," he said. "Some users want to do it every time they log out."