The Sirefef Trojan, also known as the ZeroAccess rootkit, has several components that allow it to mount an attack on all fronts when infecting a computer. Trojan:Win32/Sirefef.AC in particular is a malicious executable file that is usually a part of this malware family's attack. It's worth to be noted that Trojan:Win32/Sirefef.AC is almost never present on its own and is usually used to give support or to hide other malware on the victim's computer system. Because of this, if you suspect that Trojan:Win32/Sirefef.AC is in your computer, it is almost certain that Trojan:Win32/Sirefef.AC is accompanied with a variety of other malware threats.
Like most rootkits, Trojan:Win32/Sirefef.AC displays no external symptoms, which makes Trojan:Win32/Sirefef.AC particularly dangerous. Make no mistake about it, ESG security analysts consider that Trojan:Win32/Sirefef.AC and its associated rootkit are severe threats to your computer's security. Trojan:Win32/Sirefef.AC serves an essential function in a ZeroAccess rootkit attack, allowing this malware threat to remain on the victim's computer after incomplete deletion or after a function like system restore is used in an attempt to reverse the effects of the malware associated with Sirefef or ZeroAccess.
Trojan:Win32/Sirefef.AC is Closely Linked to Browser Hijacker Scams
Trojan:Win32/Sirefef.AC is a tiny file, just about 5.5 kb in size. Its presence in your computer will usually be detected with an advanced security program, often under an alias. Look for the strings Sirefef, ZeroAccess, or Zaccess, in the file names or detection names in order to identify malware potentially associated with Trojan:Win32/Sirefef.AC. The most common way in which a Trojan:Win32/Sirefef.AC Trojan-related infection manifests itself is through browser hijacking, particularly those kinds of browser redirects that involve changing the results of an online search (often commonly referred to as the 'Google Redirect Virus').
Trojan:Win32/Sirefef.AC is specific to the Windows operating system and cannot attack Mac OS or Linux systems. It can also be prevented by keeping your operating system, web browser and other applications fully updated in order to patch up any known vulnerabilities. Making sure to use a reliable anti-malware scanner that is also fully updated should catch any variants of Sirefef such as Trojan:Win32/Sirefef.AC before they infiltrate your computer system. Most security software manufacturers identified Trojan:Win32/Sirefef.AC in February of 2012, so making sure that your security applications are updated to at least spring of 2012 should be enough to prevent a Trojan:Win32/Sirefef.AC Trojan attack.