I don't think it is the ads on the board that are the problem, it is the links that members post. When you click on those links, you may be going to a private site that may or may not have malware/virus's/trojans attached to them.
This is where my antivirus alarms have been set off... when clicking on a random quilting site, blog, or other websites, that members have posted here, or during internet searches on my own.
I have been a member here for 3 years, and never once has anything thing that Admin has placed on the board set off my antivirus, malware, or antispy programs :D:D:D
When you open an email, even from family or friends, if they do not have a good antivirus program, or keep it updated, you open yourself up to a whole host of issues.
The same with unsolicited emails. You are better off deleting them without opening them, rather than chance inviting in a computer risk. :wink: