I have often recommended file-scanning services like VirusTotal and Jotti, which allow visitors to upload a suspicious file and scan it against dozens of commercial anti-virus tools. If a scan generates any virus alerts or red flags, the report produced by the scan is shared with all of the participating anti-virus makers so that those vendors can incorporate detection for the newly discovered malware into their products.

That pooling of intelligence on new threats also serves to make the free scanning services less attractive to virus authors, who would almost certainly like nothing more than to freely and simultaneously test the stealth of their new creations across a wide range of security software. Still, there is nothing to stop an enterprising hacker from purchasing a license for each of the anti-virus tools on the market and selling access to a separate scanning service that appeals to the virus-writing community.

Enter upstart file-scanning services like av-check.com and virtest.com, which bank on the guarantee that they won't share your malware with the anti-virus community.

For $1 per file scanned (or a $40 monthly membership) av-check.com will see if your file is detected by any of 22 anti-virus products, including AVAST, AVG, Avira, BitDefender, NOD32, F-Secure, Kaspersky, McAfee, Panda, Sophos, Symantec and Trend Micro. "Each of them is setten [sic] up on max heuristic check level," av-check promises. "We guarantee that we don’t save your uploaded files and they are deleted immediately after the check. Also, we don’t resend your uploaded files to the 3rd person. Files are being checked only locally (without checking/using on other servers." In other words: There is no danger that the results of these scans will somehow leak out to the anti-virus vendors.

The service claims that it will soon be rolling out advanced features, such as testing malware against anti-spyware and firewall programs, as well as a test to see whether the malware functions in a virtual machine, such as VMWare or VirtualBox. For safety and efficiency's sake, security researchers often poke and prod new malware samples in a virtual environment. As a result many new families of malware are designed to shut down or destroy themselves if they detect they are being run inside of a virtual machine.

Virtest checks suspicious files against a similar albeit slightly different set of anti-virus programs, also promising not to let submitted files get back to the anti-virus vendors: "Your soft isn't ever sent anywhere and the files being checked will never appear in the fresh AV signature bases after scanning," the site pledges. "On purpose in all AV-products are turned off all possible methods and initiatives of exchange of files’ info with the AV-divisions."

The proprietors of this service don't even try to hide the fact that they have built it for malware writers. Among the chief distinguishing features of virtest.com is the ability for malware authors to test "exploit packs," pre-packaged kits that – when stitched into a malicious or hacked website – serve the visitor’s browser with a kitchen sink full of code designed to install software via one of several known security holes. Many anti-virus programs now also scan web pages for malicious content, and this service’s "exploits pack check" will tell malware authors whether their exploit sites are triggering virus alerts across a range of widely used anti-virus software.

But don't count on paying for these services via American Express: Both sites only accept payment via virtual currencies such as Webmoney and Fethard, services that appear to be popular with the online shadow economy.

Investigative journalist Brian Krebs is a former reporter for The Washington Post, where he wrote the Security Fix blog. He's currently editor of KrebsOnSecurity.com.