I just took over admin for a web site that has a discussion forum. I found and cleared the problems with the main web site. Did the same with the discussion forum. Checked it in both IE and Firefox and got no virus or malware warnings. Most of the regular users are also reporting they are now getting no warnings and having no problems.

However, when I announced in social networks that the site was back in good health, I have a couple people telling me they're still getting viruses/virus warnings. One even claims she had to spend $150 to get her computer cleaned of trojans after she visited the site just yesterday. Another claims she got virus warnings in the header - even though I've removed all the added header codes (ad banners, etc. - the default header for the forum software is still there).

I am stumped as to why some people continue to have problems. I suspect an element of paranoia and perhaps some sabotage of reputation (not of the site itself).

Is there an online service that will certify a site as free of malware and viruses? I'm thinking this may be the only thing that will restore confidence in the site. I figure if there is such a thing, someone here would know about it.

depends on the warning they are getting. They may well be coming from earlier reported issues is the users have the Google toolbar installed

I don't know if users have Google toolbar installed.

The problem does seem to be only Internet Explorer users; Firefox users aren't reporting any problems. I don't get any virus warnings when I open the site using IE, but a friend just went to the site using IE and said she got 17 warning messages.

It's very difficult to isolate a problem when (a) I'm not getting the messages myself and (b) user reporting isn't very accurate.

I ran a scan on the site files and cleaned up reported problems. I don't know what else to do unless the database has an infection.

Difficult to more helpful without some specifics, but I would guess at there has been some reports of malware at your URI and some possibly third party "security" feature (Nortons IS or similar) that "plugs in" to IE is reporting this. (bit like the "phishing" warning feature of IE7+ does).

Thanks for the help, Chris.

You can try McAfee Site Advisor
http://www.siteadvisor.com/webmasters/index.html

There are several problems coming out of IE7. Comparatively, you hardly face same problems in firefox. You should use a virus scanner or a registered anti-virus every time to get rid of trojans. The problem you are facing should either be with all of trffickers or none of them. To some extent google toolbar is unreliable as well...

Thanks for the input, everyone.

Turns out this was a caching problem - clearing the cache solved all the problems.

I still have my work cut out for me to rebuild confidence in the safety of the forums, but at least I know now that I'm not going crazy!