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The pros and cons of reformatting a hard drive

In this Ask the Expert Q&A, our platform security expert discusses the pros and cons of reformatting a hard drive after an attack.

Can a virus still infiltrate a hard drive after it has been completely reformatted?

If you choose to reformat a hard drive, you are essentially creating a new, blank indexing scheme, which will make every sector available to write new files. This also makes it appear as though there are no files, directories and data on the drive. However, there is no need to panic, reformatting doesn't actually delete the binary files. While specialist programs can retrieve a lot of the "wiped" files, a virus, or any other program for that matter, is not capable of resurrecting after a disk format.

However, reformatting your hard drive and reinstalling your operating system and programs is very time consuming and it may not solve your problem of being infected by a virus or viruses. Although these viruses will be removed, they can reappear if you have not fixed the security weakness that initially infected your system. Before going the reformatting route, I would run antivirus and antispyware programs that have up-to-date signature files to ensure that your firewall settings are correct. You can also clean your computer by using the viral removal tools available from the Symantec site. I would only reformat and reinstall if you are still suffering from the virus after the checks have been completed. On the other hand, if your drive is part of a system that is used for critical or sensitive work, and it is imperative that it is free from viruses, Trojans and intruder modifications, I would seriously consider reformatting. In this case, merely determining and fixing the vulnerability may not be enough.

If you decide to reformat your hard drive, you will need to backup all your key data, ensure that you have all the original distribution media and any special drivers your system requires. You should physically disconnect the computer from the Internet before reformatting and leave it disconnected until it is fully patched and protected by a firewall. If the computer has a wireless card, remove or shield it so the computer cannot connect to any access points until it is secured. You will also need to reformat and reinstall the operating system, and install all the latest security patches before reconnecting to the Internet. A computer that doesn't have proper patching and firewall protection can be infected within seconds of being connected to the Internet.

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This was last published in October 2005

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