Now ITR e Filing with digital signature is mandatory for Individual,HUF and Firms also to whom Audit provision u/s 44AB is applicable.Income tax department has issued a notification 37/2011 dated 01.07.2011in this regard. After issuance of Notification Individual /Hindu undivided family assessees (covered under audit section 44AB)have to file ITR-4 and Firms (covered under audit section 44AB) have to file ITR-5 with digital signature.Companies are already directed to file returns through digital signature only.
Earlier(notification 49/2010) It was optional for firms,individuals ,HUF (covered under audit section 44AB) to file return through e filing mode with or without digital signature.
INCOME-TAX (SIXTH AMENDMENT) RULES, 2011 - AMENDMENT IN RULE 12
NOTIFICATION NO. 37/2011 [F. NO. 149/68/2011-SO (TPL)], DATED 1-7-2011
Read more: http://www.simpletaxindia.org/2011/07/itr-e-filing-digital-signature.html