Profits fell to £14m compared with £32m a year earlier.
That fall is partly due to the costs of last year's serious cyber attack,  which cost the company £42m.
Dido Harding, TalkTalk chief executive told the BBC: "We have significantly increased our spending on security. We take this extremely seriously."
Talktalk lost 101,000 subscribers in its third quarter after the attack, which resulted in the personal data of nearly 160,000 people being accessed.
The data haul netted email addresses, names and phone numbers. 21,000 unique bank account numbers and sort codes were accessed in the attack.
There have been six arrests in the UK connected with the hacking, all of them of individuals under 21 years old.
Ms Harding said: "I am actually very encouraged by the way the business has bounced back so strongly in the last quarter.
"The customer base has really stabilised and this is testimony to the fact that our customers really appreciated our open and honest approach and how we tried to look after them through the cyber attack."
She added that Talktalk's customer "churn" - the turnover of customers - has been the lowest in TalkTalk's history, suggesting customers are satisfied with the company's service.
TalkTalk says total revenues grew 2.4% to £1.83bn in the 12 months to 31 March.

Profits for the three months to March rose to $3.8bn (Â£2.6bn), compared with $2.1bn for the same period in 2015.
The stronger performance in Europe helped Ford to outpace Detroit rival General Motors.
Ford chief executive Mark Fields said the company had an "absolutely terrific start to the year".
Shares rose 3.2% in New York, but are still 11% lower than this time last year.
Ford's European business made a pretax profit of $434m in the quarter - higher than the total for all of last year - and substantially better than a $42m loss for the same period in 2015.
By comparison GM made a $6m loss in Europe during the first quarter of 2016, better than the $239m loss last year.
Ford remained the region's best-selling commercial vehicle brand, reflecting the popularity of the Transit and Ranger lineups.
In North America, Ford's F-150 trucks and SUVs were a major contributor to the company's profit growth.
Pretax profit in the region rose to $3.1bn, outpacing GM's $2.3bn and more than double the $1.5bn for the first quarter of 2015.
Earlier this month the company said it had set up a new subsidiary, Ford Smart Mobility, in a bid to combat growing competition from the technology sector.
Ford has been investing in driverless cars and earlier this year tested a self-driving vehicle in the snow.
Telephone and broadband provider Talktalk saw profits more than halve following a hack attack on its systems last October.
[NEXT_CONCEPT]
Ford posted a record quarterly profit following strong sales in Europe and moving more pick-up trucks and SUVs in North America.