IT security programs would probably be much worse than they are without sandboxes, which isolate programs to prevent them from being infected by hackers. A recent analysis of the Tinba malware, however, indicated that cybercriminals are getting better at monitoring users’ every movement to evade sandboxes entirely.

F-Secure researchers showed how a sample of Tinba was taking advantage of two different application programming interfaces (APIs) to avoid sandbox detection. This includes using an API called GetForeGroundWindow to look for changes in open windows on a given machine. That way, once a user has moved away from a sandbox window, for example, it would execute a runtime to infect the machine. Another API, GetCursorPos, would work similarly in monitoring the movement of a mouse. F-Secure said Tinba then looks at whether the machine it is trying to infect has enough space to run the malware.

The research is just more proof that Tinba is among the most sophisticated and innovative pieces of malware from the last few years. First discovered in 2012 and primarily aimed at the financial services sector, it has proven deadly effective in stealing data, including banking credentials and credit card information. Around the middle of 2014, Threatpost and others reported that the source code for the malware was making the rounds via an underground forum. That may have allowed an even wider range of hackers to tinker with it and develop anti-sandboxing techniques.

Perhaps even more concerning, Tinba has been growing not only in its capabilities, but also its reach. Although it reportedly began by infecting machines in smaller countries, last fall SC Magazine said it was spreading into U.S. financial institutions.

Even before exploiting APIs to avoid sandboxes, the malware was already difficult to detect, taking up only 20 KB — they don’t call it “tiny banker” for nothing. In fact, early reports of Tinba on sites like Techworld suggested that its status as such a small Trojan was one of the reasons it was able to infiltrate what are normally highly secure environments. As the years go by, CISOs and their teams are no doubt more alert, which is why tracking mouse movements and window activity may be more important. After all, even in IT security, size isn’t everything.