Trojan:JS/Medfos.B belongs to a group of malware that tries to exploit certain security flaw in Java in order to sneak into the target computer. Once inside the computer, the Trojan attempts to contact a remote server and download other malware including rogue programs. It has the capability to get inside the computer without being caught by installed anti-virus software.
Damage Level: High
Systems Affected: Windows 9x, 2000, XP, Windows Vista/7
When it enters the computer, Trojan:JS/Medfos.B makes certain changes that causes abnormality on your computer. It will have an effect on you system files and registry entries. These changes are vital for the Trojan to take control on the PC.
Once Trojan:JS/Medfos.B is running, you will notice some instant changes on the operation. Performance of the machine reduces to a half as well as your Internet connection. Internet browser will also be affected by this malware. Browser redirect and home page hijacking is observed by some victims.
It arrives as an attached file to spam email messages or links from social networking sites. Users may also obtain a code from Trojan:JS/Medfos.B when visiting web page that is compromised. It is hosted as a Java Script on some web site that will initiate the harmful script during your visit. As mentioned, the attack will take effect only if there is a way it can exploit Java in your machine.
As show in the image above, Microsoft Security Essentials keeps on issuing an alert if Trojan:JS/Medfos.B is present on the computer.
How to Remove Trojan:JS/Medfos.B
Systematic procedures to get rid of the threat are presented on this section. Make sure to scan the computer with suggested tools and scanners.
Step 1 : Download Microsoft Safety Scanner and Run a Scan
If you have previous version of Microsoft Safety Scanner that is more than 10 days old, please disregard it. Download a new copy from the official web site. Every 10 days, Microsoft will release the latest edition of this tool with updated anti-virus definitions to ensure that it will detect even most recent malware threats.
1. Download Microsoft Safety Scanner by clicking the button below and save it on your desktop. This is a free tool from Microsoft that offers on-demand scanning. It helps remove computer infection such as malware, virus, and Trojan.
2. Restart Windows in Safe Mode.
Boot in Safe Mode on Windows XP, Windows Vista, and Windows 7 system
a) Before Windows begins to load, press F8 on your keyboard.
b) It will display the Advanced Boot Options menu. Select Safe Mode.
Start computer in Safe Mode using Windows 8
a) Before Windows begins to load, press Shift and F8 on your keyboard.
b) On Recovery interface, click on 'See advanced repair options'.
c) Next, click on Troubleshoot option.
d) Then, select Advanced options from the list.
e) Lastly, please choose Windows Startup Settings and click on Restart. When Windows restarts, you will be send to a familiar Advanced Boot Options screen.
f) Select Safe Mode from the selections menu.
3. Once Windows starts in Safe Mode, locate the file of Microsoft Safety Scanner (msert.exe) that you have downloaded earlier. Double-click to run the file.
4. When it shows End user license agreement, please accept and click Next to continue.
5. On Scan Type window, please select Full scan. The tool will scan the entire system. This is ideal to detect and remove all threats that are present on the computer.
6. Click Next to begin the scan. This process will take a while to finish. Please be patient and let MSS complete the scan procedure.
7. Once the scan operation ends, it will provide a report for identified threats. Please remove all the threats.
8. Reboot the computer and run another scan after Windows boots normally to make sure that Trojan:JS/Medfos.B is gone. You may now restart Windows normally.
Step 2 : Double-check for Remnants of Trojan:JS/Medfos.B using Malwarebytes Anti-Malware
This guide requires a tool called Malwarebytes' Anti-Malware. It is a free tool designed to eradicate various computer infections including Trojan:JS/Medfos.B. MBAM scanner and malware removal tool is distributed for free.
1. In order to completely remove Trojan:JS/Medfos.B, it is best to download and run the recommended tool. Please click the button below to begin download.
2. After downloading, double-click on the file to install the application. If you are using Windows Vista or Windows 7, right-click on the file and select 'Run as administator' from the list.
3. When User Account Control prompts, please click Yes to proceed with the installation.
4. Follow the prompts and install as 'default' only. There are no changes needed during the installation process.
5. Before the installation procedure ends, MalwareBytes Anti-Malware will ask for database update, please proceed.
6. Click Finish button after installation. Program will run automatically run and you will be prompted to update if newer version of database is available.
7. At this moment, close MalwareBytes Anti-Malware and proceed with the next step.
Run a thorough scan in Safe Mode to remove Trojan:JS/Medfos.B
8. Remove all media such as floppy drive, cd, dvd, and USB devices. Then, restart the computer in Safe Mode using the procedures above.
9. Once Windows is running on Safe Mode, find the icon of MalwareBytes Anti-Malware. Double-click to launch the program.
10. Choose Perform full scan on scanner's console to ensure that it thoroughly check the PC for any presence of Trojan:JS/Medfos.B and other forms of threats. Click the Scan button to start.
11. Once the scan has completed, Malwarebytes Anti-Malware will issue a list of identified threats. Mark all threats and click on Remove Selected.
12. If it prompts to restart the computer, please reboot Windows normally.
Alternative Removal Procedure for Trojan:JS/Medfos.B
Use Windows System Restore to return Windows to previous state
During an infection, Trojan:JS/Medfos.B drops various files and registry entries. The threat intentionally hides system files by setting options in the registry. With these rigid changes, the best solution is to return Windows to previous working state is through System Restore.
To verify if System Restore is active on your computer, please follow the instructions below to access this feature.
How to Access System Restore on Windows XP, Windows Vista, and Windows 7
a) Go to Start Menu, then under 'Run' or 'Search Program and Files' field, type rstrui.
b) Then, press Enter on the keyboard to open System Restore Settings.
How to Open System Restore on Windows 8
a) Hover your mouse cursor to the lower left corner of the screen and wait for the Start icon to appear.
b) Right-click on the icon and select Run from the list. This will open a Run dialog box.
c) Type rstrui on the 'Open' field and click on OK to initiate the command.
If previous restore point is saved, you may proceed with Windows System Restore. Click here to see the full procedure.
Ways to Prevent Trojan:JS/Medfos.B Infection
Take the following steps to protect the computer from threats. Suggested tools and security setup within installed software helps prevent the same attack on your PC.