What Is a Bot? Types, Uses, and Security Risks

A bot is a software application that runs automated tasks over the internet, often much faster than a person could. Bots range from helpful tools like search engine crawlers to harmful programs that steal accounts and scrape data.

Bots now dominate the web. In 2024, automated traffic reached 51% of all web traffic, surpassing humans for the first time in a decade, and bad bots alone made up 37%, according to the Bad Bot Report.

What is a Bot?

A bot is a program that follows a set of instructions to carry out repetitive tasks on its own, without a person starting it each time. Most bots imitate human behavior, such as browsing a page or sending a message, at machine speed and scale.

Bots exist to do at scale what a person cannot: repeat a task thousands of times without tiring. That efficiency serves businesses through automation and serves attackers through automated abuse, which sets up the good-versus-bad divide covered below.

How Do Bots Work?

A bot works by running code that connects to a network and interacts with websites, apps, or APIs the way a user would, but automatically. It sends requests, reads the responses, and acts on them based on its programming.

Bots are split into two groups by intelligence. Rule-based bots follow fixed scripts and handle predictable tasks, while AI-driven bots use machine learning to adapt, hold conversations, and evade detection. Every bot connected to the internet carries an IP address that identifies its traffic.

AI-driven bots are the fastest-growing group. Generative AI lets attackers build more evasive bad bots and lets AI crawlers harvest web content at scale for training data, a major reason automated traffic has overtaken human traffic online.

Types of Bots

Bots fall into several categories based on the task they perform.

Good Bots vs Bad Bots

The line between a good bot and a bad bot comes down to permission and intent, not technology. Good bots follow the rules a site sets, such as its robots.txt file, and perform tasks the owner allows, like search indexing or price comparison.

Bad bots ignore those rules and pursue goals the owner never approved. They break into accounts, steal content, commit fraud, or overwhelm servers, and they often disguise themselves as real users to avoid detection.

How Malicious Bots Attack

Bad bots power some of the most common attacks on websites and apps. Seven patterns account for most of the damage.

Credential stuffing

Bots test stolen username and password pairs against login pages to hijack accounts. The pairs come from earlier breaches, which makes leaked credentials the fuel behind these attacks.

Web scraping

Scraper bots copy content, prices, and data at scale, undercutting competitors or stealing intellectual property. Aggressive scraping strains servers and skews analytics.

DDoS attacks

Bot armies flood a site with traffic until it slows or crashes. A distributed denial-of-service attack uses many machines at once to overwhelm the target.

Account takeover

Once a bot validates stolen credentials, attackers seize the account to drain funds, steal data, or commit fraud. Account takeover rose sharply as bots automated the process.

Spam and abuse

Spam bots post junk comments, fake reviews, and phishing links across forms and forums. They harvest email addresses and spread scams at volume.

Ad and click fraud

Bots generate fake clicks and impressions to drain advertising budgets or inflate revenue. This fraud costs advertisers billions of dollars each year.

Inventory hoarding

Scalper bots buy or reserve limited stock, from concert tickets to sneakers, faster than any human. They resell it at a markup or deny it to real customers.

Bot vs. Botnet: What’s the difference

A bot is a single automated program, while a botnet is a network of many infected devices, each running a bot under one attacker's control. The core difference is scale: one bot performs a task, and a botnet coordinates thousands of them at once.

That scale makes botnets dangerous. Because a botnet's traffic comes from thousands of different devices and IP addresses, it resists blocking, which makes it the engine behind large DDoS attacks, spam campaigns, and credential-stuffing runs. The infected devices, often called zombies, run the attacker's commands without the owner's knowledge.

The Mirai botnet shows this scale in action. In 2016, it infected hundreds of thousands of IoT devices through default passwords and launched a DDoS attack that knocked Twitter, Netflix, and Reddit offline by overwhelming the DNS provider Dyn. CISA's advisory on the Mirai threat details how the botnet spread through weakly secured devices.

How to Detect and Stop Bots

Stopping bad bots means telling them apart from real users and legitimate bots, then blocking the harmful ones.

Detection starts with behavior. Security tools watch for signs no human produces, such as thousands of requests per minute, impossible mouse paths, or logins from mismatched locations. Machine learning models score traffic to separate bots from people.

Common defenses layer several controls. A robots.txt file guides well-behaved bots, rate limiting caps requests per source, CAPTCHA blocks simple automation, and multi-factor authentication stops credential-stuffing bots from using stolen passwords. Dedicated bot management and web application firewalls handle the sophisticated cases. OWASP's Automated Threats project catalogs the full range of bot attacks and their countermeasures.

Frequently Asked Questions

What does “bot” stand for?

The word “bot” is short for “robot.” It refers to software that runs automated tasks, not a physical machine.

Are bots legal?

Yes, bots are legal, and most serve useful purposes like search indexing and customer support. Using bots for fraud, account theft, or attacks is illegal, even though the technology itself is not.

How can you tell if you are talking to a bot?

A bot often gives itself away through instant, generic, or repetitive replies that dodge specific questions. Bots respond faster than a person types and struggle with follow-up context.

Which industries are most targeted by bad bots?

Travel, retail, and financial services face the most bad-bot traffic. In 2024, bad bots made up 59% of retail traffic and drove 27% of all bot attacks against travel sites.

What is the difference between a bot and a virus?

A bot automates tasks and can be helpful or harmful, while a virus is malware that spreads by infecting files. Many bots are legitimate, whereas a virus is always malicious.

How do bad bots affect a website?

Bad bots slow site performance, skew analytics, steal content, and raise hosting costs. Heavy bot traffic crowds out real users and inflates infrastructure bills.