One 'virus' that some of my clients (and friends!) have had recently is a redirect issue.

This is when a genuine visitor searches for your site on Google for example, but when they click on the link to go to your site, it redirects them to another site. Usually something to with some enhancement pills. This seems to infect mostly WordPress installations, however I am aware of at least one website which was using another CMS.

However, if you attempt to replicate the issue yourself, you won't be able to.. nor will standard users to your site that come to it regularly. This is because the 'virus' checks if the user has been to the site before, and ignores them. This is a very clever idea, as it makes the problem hard to replicate, and fix.

If you are using Google Chrome, press Cmd (or Ctrl) + Shift + N and this will open a 'incognito window', which will mean every site will now treat you as a new visitor.

Go to Google, and search for your site. Click on the link to your site, if you're taken to your site you are fine. If you are not, you are most likely infected with a virus, and it is time to talk to your web-host regarding the issue.

Hope this helps someone!