Computer Security Symposium 2011 (CSS2011) with anti Malware engineering WorkShop 2011(MWS2011) was held on 19-21 Oct. 2011 in Toki Messe Niigata Convention Center in Niigata. About 330 visitors were there. There were 141 presentations. Almost half of them were by students, while others were by researchers. The presentations were about Malware, security of web and e-mail, signatures, authentications, cryptography (especially symmetric-key cryptosystems) and hash functions, where participants discussed actively.