F-secure is an anti-virus software. Free for 3 months then £45 per year (3 devices). If you don't have AV then I would consider getting one. Try AVG free.
I always treat unsolicited e/mails as scams, which they are most likely to be.
As I understand the matter, F-Secure (which is a genuine and trusted AV programme) does Not send unsolicited e/mails, unless one has adopted Talk Talk as a chosen ISP. Then, as mentioned by aelmpvw,
you will be offered the AV programme as a freebie. Otherwise, if purchased, it is deemed to be an expensive item and Not as good as Norton and a number of other programmes.