I received a call claiming it was from the Social Security, A recorded voice said that some fraudulent activity connected with my SS has been detected and I must call a hotline or else they will take legal measures. A scam?

Yep. Total scam. Social security won't call you like that they send you a letter. Over half of all phone calls that will be made in the USA this year are spam or scams. Especially with SS dont believe anything unless you contact them on their website (which i suggest signing up for to protect yourself), at at the facility, or have received a formal written letter from the office here in town.

https://m.youtube.com/watch?feature=share&v=8N96ORODZm8