What Exactly Is A Logic Bomb?

A logic bomb is a piece of code, or a program, which lies dormant within a system until a specific event triggers it, kind of like a ‘sleeper agent’.


Logic Bomb Triggers

There are probably an infinite number of triggers for a logic bomb that you could think of but some of the more common ones would be –

  • The host system reaches a certain pre-programmed date or time
  • A specific message is sent by the programmer or, alternatively, is not received by a certain time
  • A trigger point is added or removed from a website that the logic bomb is regularly checking
  • A file that is being monitored increases or decreases in size
  • A specific user is added or deleted from a system or database

The Purpose Of Logic Bombs

Logic bombs are deployed for a variety of reason some of which are more ‘legitimate’ than others.

For example, a software vendor could code a logic bomb into a piece of software.

This would then allow them to distribute that software as a free trial with a paid upgrade version.

If the user doesn’t pay the upgrade within the required time frame then the logic bomb could delete all the files, restrict usage of the product, or otherwise render the piece of software unusable.

More nefarious usage of logic bombs include deleting files.

For example, an employee could set one up to delete his employer’s databases should he not be able to enter a code at certain intervals, thereby ensuring he extracts a level of revenge should he ever get fired.

Another use of logic bombs is in the deployment of viruses and worms.

For example, it was widely believed that the recently infamous Confiker worm contained a logic bomb that was designed to activate or change the worms purpose on April the 1st this year.

About Lee Munson

Lee's non-technical background allows him to write about internet security in a clear way that is understandable to both IT professionals and people just like you who need simple answers to your security questions.


  1. Oh dear… what have they done Bobby???

  2. Hey Lee, do you have an extra logic bomb you could email me in a zip file? I’d like to destroy my employers mainframe hahaha;)

  3. Some of them certainly can be Col.

  4. These logic bombs sound very nasty indeed.


  1. […] There are plenty of times at the job where someone can feel unappreciated and they lash out by trying to sabotage the project (see “logic bombs“). […]

  2. […] This post was mentioned on Twitter by Ian Reynolds, Lee. Lee said: What Exactly Is A Logic Bomb? http://bit.ly/cyKzpT […]

  3. […] What made this virus especially dangerous was the fact that it had a trigger date (see Logic Bombs). […]

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