Favicons, those little symbols that convey a website’s brand or identity, should ideally make online users more confident about where they’re browsing, but security experts say they could potentially be linked to a new variation of the Vawtrak malware.

A senior developer at AVG Technologies explained in a blog post how thieves are using favicons to hide signed update files of Vawtrak. Once inside a user’s system, it can not only access bank accounts, but also steal a wide range of passwords using a malware module called Pony. Most significantly, AVG said cybercriminals are connecting to servers hidden on the Tor network using a proxy service to update the malware.

Vawtrak is by no means a new threat, but it is another example of how cybercriminals are beginning to treat malware as a product to be improved over time. Just last month, cybercriminals were sending specially formatted Microsoft Word documents with malicious macros to distribute the malware, according to Help Net Security. In this latest case, the approach has been described as a drive-by download through spam email messages that direct to malicious websites or exploit kits.

The use of Tor to keep cybercriminals’ infrastructure under the radar is also becoming standard practice. SC Magazine pointed out that the same Tor2Web proxy was used by the makers of CryptoLocker, probably because it means cybercriminals don’t have to package their malware with some client access to Tor.

Beyond the apparent ease with which Vawtrak can access bank accounts and passwords, it is becoming increasingly difficult to detect. Back in December, Sophos explained on its Naked Security blog how some variations were scrambling numbers to make them incomprehensible to outsiders and working in parallel with legitimate browsing sessions to avoid any suspicious spikes in online traffic patterns.

While the current case of Vawtrak is affecting users worldwide, a possibly separate attack may be aimed specifically at Canadian bank customers. InfoSecurity Magazine reported research from Heimdal Security that said Web injections were being used to infect more than 15,000 machines across the country with a botnet that steals screenshots and videos in order to carry out man-in-the-middle attacks.

As innovative as the makers of Vawtrak seem to be, the potential solutions to the threats it poses are decidedly less so. Other than keeping machines properly patched and hoping users don’t fall for phishing schemes and other social engineering attacks, the best security professionals can hope for is that more people come to realize even a tiny favicon can carry a lot of potential risk.