Should I reinstall OS X if my system is affected by a virus?

Question

When I purchased my Mac Mini it came with OS X Mountain Lion. I want to reinstall OS X as I fear some viruses got on the system through CDs. Is it possible to do it?

• Are there any other options to remove viruses completely?

• If I run an antivirus scan after a virus has affected the system, will it be removed as in Windows?

• Is it possible that viruses get installed through visiting some websites? I saw some tutorial that showed if we download or install something, a virus could affect the OS?

Solution

Is it possible to do it?

Yes, you can reinstall OS X Mountain Lion.

If I run an antivirus scan after a virus has affected the system, will it be removed as in Windows?

Most probably yes, but you can never be sure. Same as with Windows, the only way to be sure a virus is gone is to reinstall your operating system. If you really care about your data and want to be a hundred percent safe, you will have to wipe your hard drive and start fresh.

Is it possible that viruses get installed through visiting some websites? I saw some tutorial that showed if we download or install something, a virus could affect the OS?

A virus can find many vectors to access your system. OS X is often the victim of attacks through Java vulnerabilities, so it'd be a good idea to disable Java if you don't need it.

Often though, and I would say in most cases, a system being infected is the fault of the user sitting in front of the computer. If you download an executable file that happens to be a virus, and run that, you'll be infected as well. This is why OS X prompts you every time you open a downloaded file that could potentially harmful. Do you trust the source? If yes, open it, if not, don't.

Normally, any executables you run should not have permission to change anything on the system in a large scale. A virus could delete files you own or potentially read private data, however it will not be able to completely wreck your system unless you've given it root permissions. Basically, you do that by entering your user password. Never enter your password if you're not sure what you're entering it for.

That being said, just visiting a website is not dangerous per se. Often though, malicious websites make you download infected executables – however most of these are targeted against Windows users, since it's the most popular platform.

Keep it cool and … most importantly: Don't visit fishy websites. The words "warez", "cracks" and "serials" should make you suspicious, as well as anything claimed to be "free" when it normally costs money.

Comments

[Aaron Copley]

Also: Never, ever, ever browse the Internet as a user with elevated privileges. Keep your Admin account separate and only elevate as necessary to install software / updates / etc.

[slhck]

Well, OS X being Unix this is not as much of an issue as back in the Windows days, since elevating privileges requires you to type a password. But of course, if all you do is browse the internet, a guest account or restricted user would do too.

[Chris S]

+1 Nuke it from orbit, it's the only way to be sure.

[Muthu Muthu]

slhck , you are great..

[Aaron Copley]

It's just as much an issue under any operating system. (Modern or old, Unix or Windows.) Software has the privileges of the running user. This is the foundation of Least Privilege. "By default, applications run as the currently logged in user..."

[slhck]

Yes they do, but just because the user has superuser privileges doesn't give software those privileges automatically. That's what I meant. Otherwise, absolutely correct! @aar

[Robin Alvarenga]

@slhck If with your comment to Aaron mean it's not a risk to use an application with elevated privileges (like a browser) then you are wrong. If you mean that in general things are better because all programs are by default being run with low privileges then you are correct.

[Muthu Muthu]

@slhck if i update my mountain lion after new version is released by apple through software update, is it equal to reinstalling osx as it is mentioned in the link "reinstall OS X Mountain Lion"

[slhck]

@Muthu no, that's not the same. You should always update, but it's not the same as deleting everything and reinstalling