In almost all cases, retrofitting will be very expensive. It's useful to understand what computer security protects against, the respective defense mechanisms, and the different terminologies associated with it. Attempts to alter information with some selfish or malicious intent. Integrity attacks, it should be noted, can also be accidental. Attempts to disrupt a system's normal operations.
Several attacks fall into one or more of the categories mentioned above.
While that may seem like an expensive operation, in reality it is possible to preen the search using specialized tools. A Trojan horse attack involves planting an enemy as an insider in such a way that it's not apparently noticeable. A computer virus serves as a common Trojan horse example. They assume that they're communicating normally. To shield against security threats, there are a variety of protection mechanisms.