I'm sorry to hear you've got a computer virus. Fortunately, thousands of people deal with virus infections daily, and in most cases, the computer and all data can be restored. By following good online practice you can avoid future infections.
There are two main approaches for removing a virus:
- Use anti-virus software to perform a "deep scan and clean".
- Wipe and reinstall the computer - colloquially known as "nuke from orbit".
Using anti-virus software is quicker and easier, but has a greater risk that the virus will silently remain and cause problems later. Wiping and reinstalling is recommended for knowledgeable users. It is normally possible to keep all your data while doing this.
Using anti-virus software
If you do not have anti-virus software already there are various free options (e.g. Windows Defender, AVG Free) and many paid options (e.g. Symantec Endpoint Protection, Kaspersky Internet Security).
Make sure the anti-virus software is up-to-date.
You can then run a full scan of your computer. Some AV software calls this a deep scan. If any viruses are found, you will get the option to quarantine the affected file.
Some advanced viruses have the ability to hide from anti-virus software. To cope with this, some AV software has the ability to "scan on boot". The AV runs before Windows starts, and in this mode, the virus is crippled, allowing the AV software to more effectively remove it. Once complete you can boot into Windows as normal. Other AV software allows you to create a boot disk instead of "scan on boot".
The precise instructions for all this depend on your anti-virus software. Consult the manual for further information.
Wipe and reinstall
The basic idea is to copy all your data onto an external hard drive, then reinstall Windows. This will give you a blank - and hopefully uninfected - Windows installation. You will then need to reinstall all your software, restore all your data, and customise the settings you had before.
Before you start, make sure you have installation media and license codes for all your commercial software. If necessary, you can extract a Windows and Office product key from your installation. You can also download disk images from Microsoft - provided you have a product key.
You need to carefully backup all your data onto an external hard drive. It can be difficult to get everything. People often forget their address book and bookmarks. This is a stressful point, because once you start reinstalling Windows, you lose the ability to recover further data. As an alternative, you can buy a new hard disk, and put the old hard disk in a USB enclosure like this.
You then need to reinstall Windows, all your other software, then restore your data and settings.
You must follow basic security practice:
- Keep all software up-to-date. Secunia PSI helps you check software is up-to-date.
- Run anti-virus software, and keep it up-to-date.
- Enable the firewall (this is on by default in recent Windows versions)
Beyond this, you need to exercise care. It is difficult to explain precisely how to do this, but here is some basic guidance:
- Be careful where you click.
- Be especially careful when downloading software. Every
exe file you download gets full access to your computer.
- Take care with removable media. Some viruses have executable files that look like folder icons. But if you click them, you will be infected.
- Take care with shared drives, which may be on a NAS, or in cloud storage like DropBox.
While your computer had a virus, it is possible that all your passwords have been captured. You should at least change your passwords for online accounts that are important to you, e.g. web mail, social media, online banking. It usually isn't necessary to change low value passwords for forums and e-commerce sites.
It's also possible that credit card numbers have been compromised if you have used them on this computer. I believe this is fairly rare, and changing your cards is a (modest) hassle. Instead, hold on to your cards, keep a close eye on your statements and change the cards if fraud occurs.
If you've followed this through to the end, well done! It is not an easy process, and you will hopefully have recovered from the infection. Take care online - but don't be afraid of your computer.