HijackThis scans the computer looking for malicious software that modifies browsers' behavior.

Internet browsers (Chrome, Firefox, Internet Explorer, etc.) have become the most used programs on any PC and are, therefore, the subject of “attacks” performed by malicious software. This software is trying to take control of the browser to modify its behavior, forcing it to display web pages that the user has not requested or modify the content of web pages by embedding links that did not exist in the original web page or changing the default search engine. This will generate a bad user experience and make it impossible to find what we're searching for.

HijackThis is a tool that scans our system for this type of malicious program and generates a text report informing us about all possible threats found. Keep in mind that generated report shows all the entries that are susceptible to being a threat, but that does not mean that each line of the report constitutes a threat to our PC. If we do not know how to interpret the report, we should send it to specialized Internet forums, where users will tell us which report lines represent a threat to our PC and, therefore, can be deleted safely.

The main window will display a list of entries marked as potential threats. We can select any item in the list and delete it, but we must be careful because, as mentioned before, not all the list elements are a real threat. This makes HijackThis a program for advanced users because users with less knowledge should only use the option “generate report” without deleting any entry.

This program does not need installation and is not resident in memory, implying that it will not notify us if a new threat is trying to install. So we must scan the system with this software and detect already installed threats.

To use this program is simple; we have to press the “scan” button and wait for the results. Depending on our knowledge, we'll fix errors or send it to people with more knowledge. If we want to know the meaning of the found items, we must place the mouse cursor over each item and press the “Information of selected item” button. The entries are identified following a pattern of letters and numbers:

• R: refers to entries relating to the system's registry and browser's search and start page.
• F: refers to startup files.
• N: includes items related to Netscape and Mozilla.
• O: refers to the rest of the items.

This software has several tools that facilitate the removal of malicious software, such as, for example: deleting a “blocked” file at the computer restart or scanning malicious software in ADS areas of files. ADS refers to Alternate Data Streams, an area of files to store meta-information. The ADS are being used by some malicious software to hide from anti-malware tools.

Security company Trend Micro develops this program; it's free, and we can use it without any restrictions.