Brittany was browsing an online shopping site when a program got downloaded onto her system without her knowledge. The next day she found that her search engine had been changed, and she received pop$-$up advertisements of the shopping site she had visited the previous day. The program on Brittany's system is $\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_.$

Group of answer choices

Adware

RAT

Keylogger

Worm

Ransomware