It kind of depends on why you think it’s still lurking. If
subsequent scans still show that you’re infected, that’s pretty
obvious, but if it’s just that you’re uncomfortable and don’t know …
well, I’m not sure how to make you feel better.
Well, I shouldn’t say that. There is, in fact, one way to make sure
that you’re no longer infected. In fact, to be completely honest, it’s
the only sure way.
But you’re not going to like it.
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The rule of absolute security is this: once your machine has been
infected by anything, you can no longer trust it. At all.
The reason is that you have no idea what the infection did. What you
do know is that the infection allowed someone with malicious intent
access to your machine to do whatever they want to with it. The problem
is that there is no way to be absolutely positively certain you know
what they did, and thus no way to be absolutely positively certain that
you’ve removed it. You have to assume that your machine is still
“owned” by that malicious attacker.
‘owned’ by that malicious attacker.”
That’s both scary, and annoying.
So, the only way to know that you’ve totally deleted a
virus is either:
Reformat and Reinstall everything from scratch. The
operating system, the applications, all patches and updates, and your
Restore from a backup that was known to have been
taken before the infection occurred.
The problem is that for most folks, either of those two approaches
are impractical, or simply too much effort for the risk.
But if you’re serious about security and need to be 100% certain,
those are your options.
The more common approach is to scan with multiple
up-to-date anti-virus (and perhaps anti-spyware) products
until they all report things are clean. Yes, you do take on some risk
that they missed something, but from a purely pragmatic perspective,
nine times out of ten you’re probably just fine doing this.
As you can see, this is why we focus so much on prevention
of infection over recovery. Prevention, once in place, is significantly
less costly than recovery from a problem.