Editing Browser Helper Object (section)

== Concerns ==
The BHO [[application programming interface|API]] exposes [[hooking|hook]]s that allow the BHO to access the [[Document Object Model]] (DOM) of the current page and to control navigation. Because BHOs have unrestricted access to the Internet Explorer event model, some forms of [[malware]] (such as adware and spyware) have also been created as BHOs.<ref>{{Cite web|title=Browser Hijack Objects (BHOs)|url=https://blog.malwarebytes.com/threats/browser-hijack-objects-bhos/|access-date=2021-12-05|website=Malwarebytes Labs|language=en-US}}</ref><ref>{{Cite journal |last=Park |first=Beomsoo |last2=Hong |first2=Sungjin |last3=Oh |first3=Jaewook |last4=Lee |first4=Heejo |date=2005 |editor-last=Kantor |editor-first=Paul |editor2-last=Muresan |editor2-first=Gheorghe |editor3-last=Roberts |editor3-first=Fred |editor4-last=Zeng |editor4-first=Daniel D. |editor5-last=Wang |editor5-first=Fei-Yue |editor6-last=Chen |editor6-first=Hsinchun |editor7-last=Merkle |editor7-first=Ralph C. |title=Defending a Web Browser Against Spying with Browser Helper Objects |url=https://link.springer.com/chapter/10.1007/11427995_85 |journal=Intelligence and Security Informatics |series=Lecture Notes in Computer Science |language=en |location=Berlin, Heidelberg |publisher=Springer |pages=638–639 |doi=10.1007/11427995_85 |isbn=978-3-540-32063-0|url-access=subscription }}</ref>

For example, the [[Download.ject]] malware is a BHO that is activated when a secure [[HTTP]] connection is made to a financial institution, then begins to [[keystroke logging|record keystrokes]] for the purpose of capturing user passwords. The [[MyWay Searchbar]] tracks users' browsing patterns and passes the information it records to third parties. The [[C2.LOP]] malware adds links and popups of its own to web pages in order to drive users to [[pay-per-click]] websites.{{cn|date=May 2021}}

Many BHOs introduce visible changes to a browser's interface, such as installing toolbars in [[Internet Explorer]] and the like, but others run without any change to the interface.  This renders it easy for malicious coders to conceal the actions of their browser add-on, especially since, after being installed, the BHO seldom requires permission before performing further actions.  For instance, variants of the ClSpring trojan use BHOs to install scripts to provide a number of instructions to be performed such as adding and deleting registry values and downloading additional executable files, all completely transparently to the user.<ref>Computer Associates malware entry at [http://www.ca.com/us/securityadvisor/virusinfo/virus.aspx?id=42280 ca.com], retrieved 1/16/2009</ref>

In response to the problems associated with BHOs and similar extensions to Internet Explorer, Microsoft debuted an ''Add-on Manager'' in [[Internet Explorer 6]] with the release of [[Windows XP#Service Pack 2|Service Pack 2]] for [[Windows XP]] (updating it to IE6 Security Version 1, a.k.a. SP2).  This utility displays a list of all installed BHOs, [[browser extension]]s and [[ActiveX control]]s, and allows the user to enable or disable them at will.  There are also free tools (such as BHODemon) that list installed BHOs and allow the user to disable malicious extensions.  [[Spybot – Search & Destroy|Spybot S&D]] advanced  mode has a similar tool built in to allow the user to disable installed BHO.