Removal instructions for the CirrusCastellanus malicious browser extension
Written by Tomas Meskauskas on (updated)
What kind of software is CirrusCastellanus?
Our research team discovered an installation setup containing the CirrusCastellanus browser extension during a routine inspection of untrustworthy websites. The exact modus operandi of this piece of malicious software is unknown. It is evident, based on the permissions for CirrusCastellanus, that this extension targets browsing activity and, potentially, information concerning browser add-ons.
CirrusCastellanus extension overview
CirrusCastellanus seeks to acquire browsing-related information. This is not uncommon for malicious extensions; while the data of interest may vary, it is usually gathered for the purpose of selling it to third-parties or for otherwise abusing it for profit.
Targeted data may include: visited URLs, viewed webpages, entered search queries, IP addresses (geolocations), Internet cookies, account log-in credentials (i.e., usernames/passwords), personally identifiable details, finance-related information, and so forth.
CirrusCastellanus' permissions also include the management of apps, extensions, and other browser add-ons. As mentioned in the introduction, the current behavior of this piece of software is unknown. Some malicious extensions target specific content added to browsers with the intent of modifying it, while others seek to extract the information stored within them. To elaborate, log-in credentials could be sought from password managers, data from cryptocurrency-related extensions, etc.
CirrusCastellanus also implements persistence-ensuring techniques, specifically the "Managed by your organization" Google Chrome feature – to complicate its removal.
At the time of research, we did not observe CirrusCastellanus displaying ads or causing redirects. However, it is worth noting that adware and/or browser hijacker features may require certain conditions to be successfully utilized, e.g., compatible browser/system or user geolocation, visits to particular websites, etc. Hence, it is not implausible for this extension to have these capabilities.
Furthermore, developers of this type of software often improve upon it; therefore, potential future iterations of CirrusCastellanus could have additional/different functionalities.
To summarize, the presence of software like CirrusCastellanus on devices may result in system infections, severe privacy issues, financial losses, and even identity theft.
| Name | CirrusCastellanus rogue extension |
| Threat Type | Malicious browser extension |
| Browser Extension(s) | CirrusCastellanus |
| Detection Names (installer) | Antiy-AVL (GrayWare/Win32.Wacapew), DrWeb (Trojan.Siggen21.17666), Fortinet (W32/PossibleThreat), McAfee (Artemis!F23CECFA0555), Sangfor Engine Zero (Trojan.Win32.Agent.Vkxl), Zillya (Trojan.BroExt.Win32.4), Full List Of Detections (VirusTotal) |
| Distribution Methods | Deceptive pop-up ads, free software installers (bundling). |
| Damage | Decreased computer performance, browser tracking - privacy issues, possible additional malware infections. |
| Malware Removal (Windows) | To eliminate possible malware infections, scan your computer with legitimate antivirus software. Our security researchers recommend using Combo Cleaner. |
Malicious browser extension examples
We have analyzed thousands of rogue browser extensions. Chromium extension-loading shortcut virus and ChromeLoader are a couple examples of malware designed to infiltrate malicious extensions into browsers.
The most common types of browser infections are adware and browser hijackers; AdBlock adware, Pick Your Language, Browse Keeper – are a few examples of the former, and Quick World Clock, Coffee Ext, XI New Tab – of the latter.
However, regardless of how unwanted and harmful software operates – its presence endangers device/user safety. Therefore, we strongly recommend removing all threats immediately upon detection.
How did CirrusCastellanus install on my computer?
We downloaded an installer containing CirrusCastellanus from a dubious webpage. Malicious extensions can have legitimate-looking "official" download pages, and they are commonly spread through deceptive/scam websites. Most visitors access these webpages via redirects caused by sites utilizing rogue advertising networks, mistyped URLs, spam browser notifications, intrusive ads, or installed adware.
Another distribution technique is "bundling" – the packing of undesirable/malicious additions into the installation setups of ordinary programs. The risk of inadvertently allowing bundled content into the system is increased by downloading from untrustworthy sources (e.g., freeware and third-party websites, P2P sharing networks, etc.) and by rushing through installation processes (e.g., ignoring terms, skipping steps, using "Easy/Quick" settings, etc.).
Intrusive advertisements are also used to proliferate malicious content. When clicked on, some of the adverts can execute scripts to perform stealthy downloads/installations.
How to avoid installation of unwanted software?
We strongly recommend being vigilant when browsing since fraudulent and hazardous online content usually appears genuine and harmless.
It is essential to research software prior to downloading or purchasing it. We advise downloading only from official and verified channels. Another recommendation is to treat installation processes with caution, e.g., by reading terms, studying available options, using "Custom/Advanced" settings, and opting out of all additional apps, extensions, tools, features, and so on.
If your computer is already infected with CirrusCastellanus, we recommend running a scan with Combo Cleaner Antivirus for Windows to automatically eliminate this malicious extension.
CirrusCastellanus browser extension detail information (including permissions):
Instant automatic malware removal:
Manual threat removal might be a lengthy and complicated process that requires advanced IT skills. Combo Cleaner is a professional automatic malware removal tool that is recommended to get rid of malware. Download it by clicking the button below:
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Quick menu:
- What is CirrusCastellanus?
- STEP 1. Uninstall unwanted applications using Control Panel.
- STEP 2. Remove rogue extensions from Google Chrome.
- STEP 3. Remove rogue extensions from Mozilla Firefox.
- STEP 4. Remove rogue extensions from Safari.
- STEP 5. Remove rogue plug-ins from Microsoft Edge.
Unwanted application removal:
Windows 11 users:
Right-click on the Start icon, select Apps and Features. In the opened window search for the application you want to uninstall, after locating it, click on the three vertical dots and select Uninstall.
Windows 10 users:
Right-click in the lower left corner of the screen, in the Quick Access Menu select Control Panel. In the opened window choose Programs and Features.
Windows 7 users:
Click Start (Windows Logo at the bottom left corner of your desktop), choose Control Panel. Locate Programs and click Uninstall a program.
macOS (OSX) users:
Click Finder, in the opened screen select Applications. Drag the app from the Applications folder to the Trash (located in your Dock), then right click the Trash icon and select Empty Trash.
In the uninstall programs window, look for any unwanted applications, select these entries and click "Uninstall" or "Remove".
After uninstalling the unwanted applications, scan your computer for any remaining unwanted components or possible malware infections. To scan your computer, use recommended malware removal software.
Remove malicious extensions from Internet browsers:
Video showing how to remove potentially unwanted browser add-ons:
Remove malicious extensions from Google Chrome:
Click the Chrome menu icon 
(at the top right corner of Google Chrome), select "Extensions" and click "Manage Extensions". Locate "CirrusCastellanus" and all other recently-installed suspicious extensions, select these entries and click "Remove".
Optional method:
If you continue to have problems with removal of the cirruscastellanus rogue extension, reset your Google Chrome browser settings. Click the Chrome menu icon (at the top right corner of Google Chrome) and select Settings. Scroll down to the bottom of the screen. Click the Advanced… link.
After scrolling to the bottom of the screen, click the Reset (Restore settings to their original defaults) button.
In the opened window, confirm that you wish to reset Google Chrome settings to default by clicking the Reset button.
Remove malicious plugins from Mozilla Firefox:
Click the Firefox menu 
(at the top right corner of the main window), select "Add-ons and themes". Click "Extensions", in the opened window locate recently-installed suspicious extensions, click on the three dots and then click "Remove".
Optional method:
Computer users who have problems with cirruscastellanus rogue extension removal can reset their Mozilla Firefox settings.
Open Mozilla Firefox, at the top right corner of the main window, click the Firefox menu, in the opened menu, click Help.
Select Troubleshooting Information.
In the opened window, click the Refresh Firefox button.
In the opened window, confirm that you wish to reset Mozilla Firefox settings to default by clicking the Refresh Firefox button.
Remove malicious extensions from Safari:
Make sure your Safari browser is active, click Safari menu, and select Preferences....
In the opened window click Extensions, locate any recently installed suspicious extension, select it and click Uninstall.
Optional method:
Make sure your Safari browser is active and click on Safari menu. From the drop down menu select Clear History and Website Data...
In the opened window select all history and click the Clear History button.
Remove malicious extensions from Microsoft Edge:
Click the Edge menu icon 
(at the upper-right corner of Microsoft Edge), select "Extensions". Locate all recently-installed suspicious browser add-ons and click "Remove" below their names.
Optional method:
If you continue to have problems with removal of the cirruscastellanus rogue extension, reset your Microsoft Edge browser settings. Click the Edge menu icon (at the top right corner of Microsoft Edge) and select Settings.
In the opened settings menu select Reset settings.
Select Restore settings to their default values. In the opened window, confirm that you wish to reset Microsoft Edge settings to default by clicking the Reset button.
- If this did not help, follow these alternative instructions explaining how to reset the Microsoft Edge browser.
Summary:
Commonly, adware or potentially unwanted applications infiltrate Internet browsers through free software downloads. Note that the safest source for downloading free software is via developers' websites only. To avoid installation of adware, be very attentive when downloading and installing free software. When installing previously-downloaded free programs, choose the custom or advanced installation options – this step will reveal any potentially unwanted applications listed for installation together with your chosen free program.
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Frequently Asked Questions (FAQ)
How did CirrusCastellanus infiltrate my computer?
We acquired an installer containing CirrusCastellanus from a rogue webpage. Most visitors to such sites enter them through redirects generated by misspelled URLs, websites using rogue advertising networks, spam browser notifications, intrusive ads, or installed adware.
However, malicious browser extensions are spread using other techniques as well. Software of this kind is also proliferated via untrustworthy download channels, e.g., freeware and free file-hosting websites, third-party app stores, Peer-to-Peer sharing networks, etc.
What harm can CirrusCastellanus cause?
In general, malicious browser extensions may cause system infections, serious privacy issues, financial losses, and even identity theft. It is pertinent to mention that the exact dangers associated with any infection depend on the software's capabilities and modus operandi.
What is the purpose of CirrusCastellanus?
Like most malicious extensions, CirrusCastellanus is designed to generate revenue. However, exactly how the developers profit can vary. CirrusCastellanus has data-tracking functionalities – hence, the collected information could be monetized through sale to third-parties or otherwise abused for profit. Generally, malicious extensions generate revenue by monetizing gathered data, displaying ads, causing redirects, etc.
Will Combo Cleaner remove CirrusCastellanus?
Yes, Combo Cleaner is designed to eliminate all manner of threats. It must be mentioned that manual removal (unaided by security programs) might be ineffective. In cases where multiple malicious extensions are installed: after one is removed – the others may simply reinstall it.
Additionally, in some instances, after a rogue piece of software has been manually removed – various remnants stay hidden within the system. The remaining components might continue to run and cause issues. Therefore, it is paramount to remove unwanted software thoroughly.
Outstanding!
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