Proof of citizenship is not required to register to vote in federal elections, but some states require applicants to submit Social Security numbers and perform checks on them. However, the chief actuary of the Social Security Administration estimated in 2013 that about 0.7 million illegal immigrants worked in 2010 by using SS numbers obtained with "fraudulent birth certificates" and 1.8 million worked by using SS numbers "that did not match their name." Also, a 2002 Government Accountability Office investigation found that "the use of fraudulent documents by aliens is extensive," and in 2016, Barack Obama stated that voting records are not cross-checked against immigration databases and "there is not a situation where the voting rolls somehow are transferred over and people start investigating, etcetera."