There is a lot of selection bias in the type of people that post on those sites. The salaries are almost always deflated. Software engineers making $200k+ aren't posting on indeed.com.
Really? Last I looked self-reported numbers tend to be _inflated_ compared to govt collected figures (from tax returns and payroll reports). My intuitive understanding of this is that people being underpaid tend to not want to brag about it, even anonymously.
I guess the best way to know if you are underpaid is applying for other positions and see what kind of offers you get.