Viruses
At one time most viruses were spread through sharing of floppy disks. Later with the rise of e-mail correspondence was the primary method of delivering a Virus to you, now with the internet connectivity of everything, the internet/ hacked web sites are the number one threat. Just because e-mail is no longer the prime source does not mean you can ignore it. Some very nasty malware is spread with social engineered e-mails that entice you to open attachments that are not what they appear. The very nasty Cryptolocker malware that encrypts your data files is spread primarily via e-mail.
Virus Scanning Software
It used to be that everyone was concerned with "Viruses" now there are variants that are not "viruses " in the traditional sense. Malware is any software that you may be tricked into downloaded and installing that later has negative result for you and your computer.
Beware of Sender
Even with up to date anti-virus software, you should beware of any e-mail sent to you with an attachment that you do know know who the sender is. There is a delay between the time that a new virus is discovered and the time that the Anti-Virus software is updated so try not to be the one that "discovers" the virus.
If you get a virus
If you do get a virus (or you suspect you have one), do a full system scan with your Anti-Virus software. If it finds anything, have it first try to Clean the file, but if it cannot you need to quarantine or delete the file. If it is a system or critical file you will have to restore it from a clean backup. If a Virus is found you should also go to your software suppliers web page and look up the virus it found and then look at the removal method. Then look at your system and verify that the virus is eliminated, or do the steps to remove the virus.
I meant to get Anti-Virus...
If you are running without Anti-Virus software or you virus file is too far out of date and you get infected, you can still run some free scanners to check for viruses. The best of these is Trend Micro's Housecall, It allows you to so a full scan of your system over the internet. McAfee also has a program called "Stinger""Stinger.exe" that you can download to detect many of the more common viruses. It will look for and remove several (43 as of 2/5/2006) of the more common viruses.