Logic Bombs Explained2

Logic bombs are lines of software code that will disrupt normal use when certain conditions are met. These conditions commonly include specific dates and times, actions performed by the user, and commands sent from an outside source such as a hacker.

Why Many Viruses Contain Logic Bombs

Many computer viruses contain logic bombs because it allows them to spread from computer to computer without detection. When a programmer creates a virus, he or she usually wants it to infect a wide number of computers before it performs its assigned task. Inserting logic bombs into the virus program’s code that instructs it to lie dormant until a certain date, therefore, makes it possible for the virus to spread farther before those who have been infected even recognize that they have contracted an unwanted piece of software.

Common Virus Logic Bombs

Viruses that contain time sensitive logic bombs are usually designed to become active on significant dates. A virus designed to wipe hard drives clean, for instance, might contain a logic bomb instructing it to perform its intended task on 9/11. Similarly, a virus that has been designed to display a clown face after it has performed a harmful deed might contain a logic bomb instructing it to activate on April Fool’s Day. Hackers seem to think that they have a good sense of humor. Those who have been affected by their crimes usually disagree.

Logic Bombs in Proprietary Software

Not all logic bombs are found in viruses. In fact, some of the most popular logic bombs were written into proprietary software by programmers who wanted to secure their work positions or hold their employers hostage.

Many companies have found logic bombs hidden in their source code by opportunistic programmers. For instance, an employee of General Dynamics inserted a logic bomb into the company’s software in 1992. The logic bomb was designed to delete rocket information that was vital to the company’s defense contracts. The employee’s plan was to quit his position before the logic bomb went off, and then return to General Dynamics as a highly paid consultant to fix the problem. Other programmers working for the company caught the logic bomb well before it affected the software, though, and the employee was arrested by authorities for attempted fraud and computer tampering.

Logic Bombs are Unknown to Software Users

Many programs contain source code that will interfere with normal operations after a certain date. This allows companies to provide clients with free trial versions that will cease to function after a certain amount of time has elapsed. Although this code essentially performs the same function as a logic bomb, it does not carry the same name. By definition, logic bombs have been inserted into software code without the user’s knowledge. If you download a free trial version of antivirus software, for instance, then you know it will only function for a certain amount of time. It does not, therefore, meet the criteria of logic bombs. If, however, you purchased software and it ceased to function because of hidden code, then it would qualify as a logic bomb.