Malware
Malware (a portmanteau for malicious software) is any software intentionally designed to cause damage to a computer, server, client, or computer network. Malware does the damage after it is implanted or introduced in some way into a target's computer and can take the form of executable code, scripts, active content, and other software. The code is described as computer viruses, worms, Trojan horses, ransomware, spyware, adware, and scareware, among other terms. Malware has a malicious intent, acting against the interest of the computer user—and so does not include software that causes unintentional harm due to some deficiency, which is typically described as a software bug.
HijackThis
HijackThis (also HiJackThis or HJT) is a free and open-source tool to detect malware and adware on Microsoft Windows. It was originally created by Merijn Bellekom, and later sold to Trend Micro. The program is notable for quickly scanning a user's computer to display the most common locations of malware, rather than relying on a database of known spyware. HijackThis is used primarily for diagnosis of malware, not to remove or detect spyware—as uninformed use of its removal facilities can cause significant software damage to a computer. Browser hijacking can cause malware to be installed on a computer.