I recently installed BitDefender and it wouldn't open. Their support stated I had a csrss.exe trojan file. Task bar shows there are 2 of this file running. However, properties tab shows both are in win 32 and both have same file version number and publisher is Microsoft. One version shows about 1 mb and the other 5 mb use with 0 cpu. PC runs fine other than BitDefender, previously Norton Security Suite had been running fine with it and Avast installed and opened without issue. OS is win7 home premium 64 bit.
One of them may actually be legit. The legit one will be in C:\Windows\System32\csrss.exe
Run a scan with malwarebytes or another trusted antivirus client like ESET. I love malwarebytes, as it catches almost everything and can remove a lot of stuff on your system.
See this site.http://www.liutilities.com/products/wintaskspro/processlibrary/csrss/