Recent years have provided clear evidence that critical infrastructuresCritical infrastructure are increasingly at risk of being targeted by malicious attacks. As infrastructures provide essential services that are vital to the functioning of society, such as energy supply, transport, water supply, healthcare and communication systems, their protection can be a particularly important factor. Some infrastructures perform such a specific function for a country or region that the temporary or permanent loss of their services could force fundamental changes in the area. These are critical elements whose protection must be designed with multiple safeguards to ensure that their operationOperation is uninterrupted. The organization of external physical protection is not a simple task for such a facility, but the preventionPrevention of internal sabotageSabotage is even more difficult. Blast attacks are a particular threat to these systems, as they can cause serious damage to infrastructure, human lives and the economy in a short time. The perpetrators of attacks are often external actors, but increasing attention must also be paid to the threats posed by internal perpetrators, as advances in technology open up new opportunities not only in the securitySecurity domain but also, unfortunately, in the case of malicious attacks. My aim, even with this publication, is to raise awareness of insider offendersInsider offender as a source of danger and the risks of their presence.