All HYIPs are scams and they are easy to spot - any site that offers more than 10% per year is most likely a scam... so do some research. www.badbitcoin.org is a good place to start.
If you do want to invest in them, find a good HYIP monitor and get in early. The problem is that most HYIP monitors don't invest and are actually paid by the HYIPs to report falsely. But ultimately, NEVER invest/gamble more than you can afford to lose.
I run www.stacksofcoin.com which is a site dedicated to finding them, and I invest my own bitcoin to verify if they are paying or not. Sounds insane, but there are literally hundreds of these sites and the majority are instant scams - many of which can easily be identified. Generally, the higher the return, the more likely they won't pay at all.
For the record: 10bit ran for 28 days (280%), 15bit is on day 24 (240%) so although they are scams, you can sometimes get lucky.