Linux, which comes from Unix, is much better designed and implimented than Windoze and follow the design and principles of real operating systems. I could go on for a long time on this :-).
The first being that you can use the system as a non-admin user, which means that the system is protected from the user and so that limited harm can come from users. While there will always be security issues which allow for breaking into the system, it is much less likely on Linux. There are programs, including from M$, which will not run on Windoze if you are not the admin user, but if you run as the admin user then you can really mess up the system. There are a lot of security issues with Windoze too.
Yes, there are viruses, but in general this is not an issue and I have not had a problem and not heard of anyone who has. You should not read html mail, which is a security issue. Also you should avoid attachments. Since most problem attachments are Windoze executables, this is not an issue with Linux since they won't run.
There is firewall software which comes with most Linux systems. It is best to also have a hardware firewall though.
No problem with spyware or malware.
So, you really don't need a Linux virus scan or spyware remover. The firewall is builtin, but a hardware firewall router is good (for any platform).