In reply to JohnnyW:
In general having good internet sense is more important than a paid-for anti-virus.
- Don't ever run or download executable files (.exe, .jar, .bat, .ps1, loads more. Be especially vigilant if your operating system hides extensions)
- Don't open emails/attachments or click on links you aren't expecting.
- Take multiple backups of important documents regularly (store some off-site, and encrypted if it's sensitive data).
- Hover over all links to see if they're reputable/expected (google a link to see what others have said about it).