Do not fall victim to scam/fake tech support calls

Seems people frequently get phonecalls at home, claiming to be from
some PC support organization, saying your computer has been identified
as causing problems: slowing the internet, or sending spam or viruses.
They then offer to "fix" the problem for you, maybe for free or more
likely asking for payment.

These calls are all scam, fakes. - How could the caller know your phone
number? There is no way a computer user can be identified this way
(other than by asking your ISP provider of your internet connection,
who would not breach the confidentiality of their customers). - If your
computer was causing problems then that would only be known to your ISP,
and it should be them cutting off your internet connection and
contacting you to fix the problem before connecting you back.

Some of these "fixes" are benign, doing some harmless "work" then
requesting payment. But some involve installing trojan software on your
computer: software that sends spam, or maybe they search your computer
for any stored passwords or install keyloggers to trap any passwords
used in future, to access your email or netbank accounts, or maybe they
would hijack active connections to your email service or netbank, and
send spam or take your money.

If you think you may have malicious software on your computer, then
re-install from scratch: wipe and re-format the hard disk, and
re-install everything from original CDs. Do not use your computer until
you have cleaned it: do not allow it to connect to the internet until
then. Change all passwords and PINs that you may ever have used on your
computer, and change all passwords that were the same as those you used
on your computer e.g. for ticketek.com.au .

Some writeups on such fake calls (or google for more):

http://isc.sans.edu/diary/13879
http://www.pcworld.com/article/230715/avoid_getting_scammed_by_fake_techsupport_calls.html
http://www.microsoft.com/security/online-privacy/avoid-phone-scams.aspx
http://www.computerrepairtips.net/2012-update-to-the-microsoft-phone-call-scam-about-a-virus/ 
http://www.smh.com.au/nsw/dishonest-tree-loppers-pruning-savings-of-elderly-in-scams-20120902-258jq.html

See also: 

http://www.maths.usyd.edu.au/s/lscnitm/psz-CareOfYourUnikeyPassword 

Cheers, Paul