My site had more than 10000 unique visit per day but after getting multiple DMC notices in Google webmaster tools my site visit down to 2000 unique visit per day. Does it's effect of DMCA notices or something else? My site is a warez direct download site.
Yes it will effect your website ranking as DMCA is Digital Millennium Copyright Act. Some content of your might be copied from other or vice versa may also happened may be but the main thing is Yes it will effect rankings of your website.
Of course, DMCA might have deindexed many pages of your website from search engines which in return will decrease your website traffic to a high extent. Better remove the copied content and get your reconsideration ready.
Did you check how many pages or content was removed from search engine after the DMCA notice to your website?