This can refer to states as well as to private companies.
At first view, the term 'economic security' seems to be a contradiction in itself in liberal economies, since capitalism is based on insecurity. It refers to doctrines and policies, consisting in preventing and avoiding disruptions in the life of firms or, more often, of states.
As our globalisation is firstly an economic process, it is understandable that security has shifted from the military to the economic. Economic security takes particularly into account the new risks occurring from the combination of the globalised competition and the incredible new role of information, for example threats on data, attacks on public research centres, attacks from financial predators against state currencies (like in UK by George Soros in 1992, at a time when capacities of information were even less developed), stock market manipulations, etc...
And States build up new legal tools in order to protect their economies from predators, such as the US CFIUS since 1975 or in France, a minimum version in 2005. The question is to reach an acceptable balance between security and protectionism.