Trojans are malicious files that don’t have any type of included distribution technique (unlike viruses or worms). Although some trojans are disguised as benevolent files that are distributed via spam and social networking routes, others are installed without your knowledge by script-based security exploits or other PC threats. Although trojans don’t distribute themselves, trojans are often used to distribute other types of harmful software; in fact, two popular subcategories of trojans (the trojan downloader and trojan dropper) are designed expressly for such attacks. Our malware researchers encourage you to scan your entire PC if you think you’ve been victimized by a trojan, since the presence of a single trojan can also mean the presence of many other types of malicious software.
Although already a common type of PC threat, trojans are only expected to become more prolific than before due to the increasing popularity of botnet-based trojan attacks. These attacks use infected PCs en masse to crash arbitrary websites and typically also grant criminals a high level of access to the computer via a backdoor. Many trojans launch themselves automatically and may conduct their attacks without requiring any form of prompting on the victim’s part.
Common Symptoms of Trojan Attacks
Symptoms of a trojan infection may be very obvious or not visible at all, since its payload may include any of a variety of attacks. Although a trojan’s basic structure does use an independent file, trojans aren’t guaranteed to show up in memory-viewing applications (due to the potential for their code being inserted into other processes at system startup). Some trojans may also conceal their files by changing system settings that are related to Windows Explorer or Hidden-flagged files, and often will keep their files in sensitive locations like your operating system directory.
Trojans that include spyware-related functions, such as banking trojans that steal bank account information are unlikely to show obvious symptoms since their aim is to avoid being noticed. However, trojans that include downloading or installing functions can also be indirectly detected by the visible symptoms of the other PC threats that they install such as the fake pop-up alerts that are common to scamware programs. Trojans that redirect your browser to harmful sites or promote websites by other browser-altering methods, such as changing the homepage, are also common and easily detectable. However, since many trojans include multiple types of attacks with varying degrees of observability, our malware researchers don’t recommend ignoring the help that an anti-malware product can provide when trying to detect or remove trojan infections.
The Consequences of a Trojan Infection
Unlike some other types of harmful programs, trojans aren’t able to infect other computers in a direct fashion. Nonetheless, other PC threats may install trojans by exploiting viable access routes, including removable media and wireless networks. Besides the possibility of infecting other PCs, your PC may also suffer from a range of different attacks. One of the most common trojan attacks is that of a browser redirect or hijack, which forces your browser to display unwanted, irrelevant and potentially hostile websites. While some trojans are only able to affect these changes in specific types of web browsers, many trojans will use one-size-fits-all attacks, such as Hosts file changes, that can hijack any type of browser.
Regardless of their other functions, trojans are usually designed to create serious security issues for the infected PC. Standard attacks include disabling security features, opening a backdoor that allows criminals to control your PC via IRC or other methods, stealing personal information, exploiting your computer’s resources from crimes ranging from DDoS attacks to bank account fraud, and, of course, installing other harmful programs.
One of the most common reasons for a failed attempt to delete another PC threat is a failure to detect and remove the trojan that installed it during a system scan. Because of this issue, our malware analysts always encourage you to scan your PC as thoroughly as possible whenever you’re dealing with any type of harmful software, since a limited scan may allow a trojan simply to reinstall its payload anew. Reinstallations of trojan payloads are usually observable after a system reboot or after an afflicted program (a web browser, etc) is closed and reopened.
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There are currently 9,350 trojans program(s) in our database.