The Open Web Application Security Project (OWASP) is an open community dedicated to spreading knowledge on designing secure computer applications. On the 10th of September 2009 in Trinity College in Dublin, they will be holding their first Irish Application Security conference:

"OWASP Ireland AppSec 2009 Conference" - https://www.owasp.org/index.php/OWASP_Ireland_AppSec_2009_Conference

While at their site, please have a browse of their excellent guide to Web Application Penetration Testing:

"Web Application Penetration Testing" - http://www.owasp.org/index.php/Web_Application_Penetration_Testing

Their full application security testing guide (~350 pages worth) in PDF format is available for free download here:

"OWASP Testing Guide v3" - http://www.owasp.org/images/5/56/OWASP_Testing_Guide_v3.pdf

Should be an interesting event!

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Updated 2021 : note that the above post was originally published in 2009, but is left here for archival purposes. Most of the above links are now broken (as the security world moves fast), so I have unlinked them.