A computer without virus protection can be taken over in minutes

Today I went to visit a new customer. His brand new computer took forever to boot, and after a few minutes would crash.
What Happened
He set up computer
He rang friend to help him install Anti-viurs and Anti-spyware software
While waiting for friend he surfed the net for about 20 minutes
Friend arrived, shut down computer, restarted to install programs
Computer took forever to boot and crashed
He called us.
Found computer was full of viruses
We had to:
Reformat computer
Install firewall, virus and spyware protection
Surfed net
Computer fine.
Conclusion
Don't go online without adequate, up-to-date protection

Larry