Let F be a secure blockcipher with block length n$.$ Consider the following message authentication code generation

algorithm from F:

MAC. On input a secret key k of F and a message M in $\{0,1\}$ nl $,$ the algorithm first parses M as l blocks m $1,$m $2,...,$m l $.$

Then it computes t i $=$ F k $($m i $)$ for i in $[1,$l$]$ and outputs the tag T$=($t $1,...,$t l $).$

Please justify why the scheme is not secure$.$ You should give three different types of attacks.