Malicious hackers beware: Computer security expert Joel Eriksson might already own your box.

Eriksson, a researcher at the Swedish security firm Bitsec, uses reverse-engineering tools to find remotely exploitable security holes in hacking software. In particular, he targets the client-side applications intruders use to control Trojan horses from afar, finding vulnerabilities that would let him upload his own rogue software to intruders’ machines.

He demoed the technique publicly for the first time at the RSA conference Friday.

“Most malware authors are not the most careful programmers,” Eriksson said. “They may be good, but they are not the most careful about security.”