Free antivirus programs are all different just as every paid for antiviruses differ. The main difference between a paid for antivirus and a free antivirus is the quality of protection.
Paid for protection generally offers additional services such as email protection against spam, safe file downloads, priority updates and online banking security. A free antivirus generally only protects your computer files against viruses and sometimes spyware.
While free antivirus programs give you some value, they don’t have everything that a paid security application can offer. So it is better to invest in a paid for antivirus as your computer will be better protected.