Sirefef (Virus Removal Guide) - updated Dec 2019

What is Sirefef?

Sirefef – prolific malware that seeks to open a backdoor on the host machine

Sirefef is a dangerous rootkit that can disable your anti-virus software and remain hidden on Windows OS for months

Sirefef, or otherwise known as ZeroAccess or max++, is a malware-dropper that is known for its ability to hide itself on the infected computer. Numerous versions of the threat have been released over the years, although its main function is to gather relevant information about the machine and then use it as a tool to insert additional malware payloads. Rootkit.sirefef.spy distribution methods can vary, although it is usually proliferated with the help of other malware, such as Necurs Trojan.

Sirefef virus is a multi-functional malware, meaning that it employs several modules that perform different tasks on the system. For example, one component is set to open a backdoor, another one – block the firewall and security software, the next one can be used for downloading malicious files and updates from the internet, and so on. Besides, Rootkit.sirefef.spy trojan can also intercept and redirect HTTP traffic^[1] to pre-determined sites, consequently generating ad revenue for the attackers.

Because Rootkit.sirefef.spy is a Trojan and its functionality mainly consists of background activities, it can remain on the system undetected for days or even months. However, because some variants of the virus are known to redirect traffic to unknown domains, aggressive ads and redirects on Google Chrome, Mozilla Firefox, Internet Explorer or another browser can serve as a good sign of system compromise.

However, be aware that the Sirefef rootkit is not the only threat that can cause browser redirects, as it is also a functionality of adware, as well as browser hijackers, which are both much lesser threats than Rootkit.sirefef.spy Trojan. The best way to check for malicious activity is to scan the computer with anti-malware software, such as SpyHunter 5Combo Cleaner, Malwarebytes, or another reputable security program.

Other symptoms that might be related to Rootkit.sirefef.spy infection includes (although users will rarely experience anything at all, making the detection and Sirefef removal a much more complicated task):

• High CPU or memory usage
• Crashing applications or Windows
• Overall slow computer operation

It is important to note that Sirefef Trojan can disable some security applications post-infection, which only increases its prevalence n the infected device. Due to this, as well as the low occurrence of signs of the infection, users might not be aware that they are infected for weeks or even months. This is why regular computer scans with anti-malware are so important. As evident, if you have an anti-malware installed and it is not performing pre-determined scans, there is a good chance that malware like Rootkit.sirefef.spy has disabled it.

Sirefef is a relatively old malware strain that consists of multiple variants released over the years and possesses different functionality, such as installing other malware, stealing sensitive data, intercepting online traffic, etc.

To remove Sirefef rootkit and to prevent from stopping the anti-virus, experts^[2] advise accessing Safe Mode with Networking and performing a full system scan with anti-malware software. The Safe Mode launches with only necessary drivers and system components, disabling malware' functions.

However, be aware that rootkits and other malicious software might permanently damage system components on Windows. To repair that damage done by viruses, we suggest employing a PC repair tool ReimageIntego.

Infection routine

As previously mentioned, there have been multiple Sirefef variants released over the years, and each possesses some differences from another version, and distribution, prevalence, and obfuscation techniques may vary.

Some of the variants were noticed to come as an executable GoogleUpdate.exe – it is very common for malicious actors to disguise the primary executable under legitimate names to prevent users from being suspicious. The executable is placed into a newly created folder inside the %ProgramFiles% and %APPDATA% directories, begging the infection routine.

Rootkit.sirefef.spy also initiates changes inside Windows registry,^[3] modifying the following keys:

HKCU\Software\Microsoft\Windows\CurrentVersion\Run
HKLM\Software\Classes\clsid\{5839fca9-774d-42a1-acda-d6a79037f57f}\InprocServer32

Sirefef also creates a separate folder here multiple files are dropped, and the malicious code inside is used to communicate with other infected devices as well as attackers' servers via peer-to-peer. This ensures that hackers can enable new functions or update malware when desired remotely.

Rootkit.sirefef.spy tampers with system drivers by replacing legitimate ones with malicious ones. These drivers might be picked up by AV vendors as Virus:Win32/Sirefef or TrojanDropper:Win32/Sirefef.B. Additionally, the malware turns off various system components that are vital to secure OS, including Windows Firewall, Windows Update, RemoteAccess, etc.

Multiple Av vendors detect Sirefef as Rootkit.sirefef.spy, Win32/Sirefefm and other names

Pirated software installers and software vulnerabilities are the most common attack vectors

Most of the users will come close to malicious attacks when using Windows computers, but whether they infect them with malware depends on multiple factors, and the most important one is awareness. As evident, acting responsibly online and secure the OS with powerful anti-malware software will bring the best results.

First thing's first: do not download pirated software, as well as keygens/cracks that can enable full version of the program that is otherwise not free. Torrent and similar P2P networks are known to be insecure as not much effort are put into protecting users on those sites. In fact, some website owners allow malicious actors to insert JavaScript-based ads that would download and install malware automatically (by exploiting software vulnerabilities).^[4]

To avoid the latter, you need to ensure that all your browsers and the operating system are running the latest versions. For that, you should never delay the updates and rather enable the auto-update feature.

Access Safe Mode to remove Sirefef virus

Trojans are very malicious cyber threats, so it is important to remove Sirefef from your computer because it may not only use it and your Internet resources for illegal purposes, it can also try to delete your valuable files, steal your sensitive information and so on. Additionally, it may open a remote control connection to your PC and let additional threats inside your computer.

When trying to perform Sirefef removal on your system, it may kill your anti-spyware and its processes. The easiest way to bypass this functionality is by entering Safe Mode with Networking, as explained in the instructions below. Once inside, you should employ the most up-to-date anti-malware tool and run a full system scan.

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