Bot is short for ROBOT which are automated scripts that react with your web-service or web site. Bot is a member of Malware Family. But bots can be used for good purpose. Some bots are used In instant messenger, online gaming interface and analysis.
Bots are mainly used by search engines to map your site and index rank your website.
Bot programs runs automatically without a user as per schedule script for that bot. Bot mainly gather information about web crawlers or interact with instance messaging(IM) or internet relay chart(IRC).
Some bot scripts have ability to interact with server . Bots with high scan rate can cause high network consumption which Can damage network servers. Some bots have ability by which hacker can get passwords ,information, log and packet information for your site.
To prevent these Malware bots Enable a protective firewall, Use a secure backdoors, use protective exploit, prevent unknown programs from crawling your secure web pages.
Constant update of your web site helps in blocking unwanted bots. Check your site logs regularly to detect an unwanted activity from new bot. If you know your user agent and from which particular IP your bots are coming from you can block them in your “.HTaccess” file.