bug
A bug is a software error: the program does not do what its creators intended, resulting in wrong output, crashes, or strange behavior.
In plain terms
A bug is a flaw hidden in software. It is like a typo in a recipe: if the cookbook says a cup of salt instead of a tablespoon, the chef follows the instructions exactly, yet the dish is inedible. The computer executes literally what was written, even if it makes no sense.
A bug does not mean the machine is broken. The hardware is fine; the program's instructions are faulty or incomplete. Therefore, the fix is not repair work but rewriting the program code, which you then receive as an update for your phone or computer.
In the AI era, the word matters because coding agents write buggy code just like humans, only much faster. Meanwhile, they increasingly assist in finding and fixing errors.
Many bugs are reproducible: the same error occurs for the same step, greatly aiding repair. However, there are also intermittent, hard-to-catch bugs, such as when two processes access the same data simultaneously. This differs from an AI model's error: the model may give a good answer to the same question at one time and a bad one at another, not due to a faulty line of code but due to the model's operation.
How it works
- Origin: the developer (or a coding agent) makes a typo, misunderstands the task, or fails to consider a rare situation, such as someone leaving a field empty.
- Dormancy: the bug often goes unnoticed for weeks or even years because it only surfaces under certain conditions, for example on a leap day or with a very long name.
- Discovery: a tester, an automated check, or a user encounters it and reports it. This is the bug report.
- Debugging: the developer attempts to reproduce the error, then traces step by step which line of code causes it. This is called debugging.
- Fixing and verification: the faulty part is rewritten, retested to ensure the fix did not break anything else, and released in an update.
An everyday example
You try to pay in the banking app, but nothing happens when you press the 'Send' button, or the app simply closes. A few days later, an update arrives with the description: 'bug fixes'. This was a bug that was found and fixed in the meantime.
Who is affected
A common misconception
Limits and risks
- Testing can only show that there is a bug, not that there is none. With complex software, total bug-free status cannot be guaranteed in practice, and even with mathematical verification, only certain properties can be proven.
- AI-written code may appear confident and organized, yet it can contain hard-to-detect bugs, so do not trust it without verification.
- A fix can introduce a new bug elsewhere, so after an update, something that previously worked may break.
- Certain bugs open security vulnerabilities that attackers can exploit, so delaying updates poses a real risk.
Similar, but not the same
- hallucination – Hallucination is an AI model's confident but fabricated response, arising from the model's operation rather than a typo in the code, so it cannot be fixed by rewriting a single line.
- vulnerability – A vulnerability is a weakness that can be exploited for attack. It is often caused by a bug, but can also stem from poor configuration or design flaws. Most bugs are not security issues, yet they can still cause serious harm.
- hardverhiba – In a hardware failure, the device itself breaks down physically; in a bug, the device is intact, only the program running on it is faulty. Chip design flaws are also called bugs; an example was the Intel Pentium processor's 1994 division error.
Related concepts
szoftver, software development, software quality
security vulnerability, regression, collapse
debugging, testing, update, coding agent, hallucination
A brief history
The word "bug" (insect) was used by Thomas Edison for technical faults. In an 1878 letter to Tivadar Puskás, he referred to flaws in his inventions this way. In computing, a 1947 incident made it famous: a moth stuck in a relay of the Harvard Mark II computer was taped into the logbook by operators as the "first real bug". The joke worked precisely because the word already meant a fault.
Where things stand
Bug is an everyday core term in software development, and it is common in ordinary speech too. At the end of 2026, coding agents are both a new source of bugs and established helpers in finding and fixing them.
In the news
- Bug report alleges Claude Code writes user's email address into User-Agent headerNov 5, 2026 · Code
- OpenAI's GPT-6 Cyber finds 81 Firefox and 948 Linux flawsNov 2, 2026 · Code
- AI bug reports swamp maintainers as OpenAI offers advice and Firedancer sets a feeOct 27, 2026 · Code
- Claude reportedly proves safety properties in compiled code of 123 open-source librariesOct 26, 2026 · Code
- Greptile: DIY AI code reviewer costs $3 to $25 per pull request and still misses the key bugOct 26, 2026 · Code
- Flood of AI-found bugs: OpenAI outlines a five-stage disclosure planOct 19, 2026 · Code
- AI code review finds bugs, delaying PostgreSQL 19Oct 19, 2026 · Code
- BMW uses AI to detect assembly defects on its production linesOct 18, 2026 · Ipar
Also known as
bug · szoftverhiba · programhiba · programming error · software bug · software bug · defect · glitch
This entry was machine-edited and has undergone machine expert review; the “In the news” section updates automatically from Agent Age stories.