Abstract: This paper presents and evaluates a methodology for the emulation of software faults in COTS components using software implemented fault injection (SWIFI) technology. ESFFI (Emulation of Software Faults by Fault Injection) leverages matured fault injection techniques, which have been used so far for the emulation of hardware faults, and adds new features that make possible the insertion of errors mimicking those caused by real software faults. The major advantage of ESFFI over other techniques that also emulate software faults (mutations, for instance) is making fault locations ubiquitous; every software module can be targeted no matter if it is a device driver running in operating kernel mode or a 3rd party component whose source code is not available. Experimental results have shown that for specific fault classes, e.g. assignment and checking, the accuracy obtained by this technique is quite good.