Security is what we worry most about at Find Big Mail (even more than our quest to solve your almost out of space problem). Today we discovered that two security sites, Norton Safe Web and McAfee SiteAdvisor, have both done independent scans of Find Big Mail and confirmed that our site is safe according to their detailed checklists. We didn't ask or pay for these assurances in any way, so its nice to see this independent analysis.
We must admit, that after we first saw these, we figured it would be a simple scan of the website for common backdoors and scripting problems. However, closer reading of the criteria shows that they do things like provide unique email addresses and then make sure that we don't start spamming them -- very hard for us to do as we don't store any email addresses! They also check for things like popups (we don't have any) and malware (none of that either of course!) and cookie usage (the bare minimum, mostly what Google sets during authentication).
We notice from the site analytic data that sometimes people search for terms like "FindBigMail security" and we're glad that others share our concern. If you have any questions about our security practices that aren't already publicly posted, definitely get in touch with us.