How a Cyber Attack Compromised a Bookkeeper's Security

CREATED BY ALISON MEAD Published: 12/05/2025 @ 09:01AM #cyberattack #cybersecurity #bookkeepers #dataprotection #scamawareness

When a cyber attack struck a bookkeeper friend of mine, it revealed the hidden dangers of downloading files from seemingly trustworthy sources. In this blog post, she chronicles the experience, offering essential insights into recognising threats and protecting sensitive information in the digital age ...

Cyber attack strikes hard, Codes and firewalls no match, Silent destruction

It all began with a simple login attempt. She went to access her agent account for self-assessment and CIS, only to be met with an unexpected roadblock: she was locked out. A call to HMRC revealed that her account had been suspended due to suspicious activity. Not exactly the kind of Monday motivation anyone hopes for.

Thankfully, two anxious weeks later, her
access was reinstated!

Naturally, the first thing she did was change her password. But when she checked the account, she noticed something alarming - an unfamiliar name had been added to her self-assessment section, and one of her CIS clients had mysteriously disappeared. She sprang into action, deleting the intruder, updating her password again (better safe than sorry), and launching a full investigation.

Being diligent and responsible, she reported the breach to the Information Commissioner's Office (ICO) and her professional body, the Institute of Certified Bookkeepers (ICB). She also took on the daunting task of contacting every single client and subcontractor who might've been affected - around 90 people in total. A full system scan revealed the presence of trojans. Not exactly the kind of house guests you'd want on your computer.

But here's the kicker – she was cyber-aware. She used a password manager. She kept her systems up to date. So, how on earth did someone breach her defences?

The answer came in the form of an AccountingWEB newsletter. The article that caught her eye was called, “Agent accounts under attack in new cybercrime wave”. It described a disturbing trend of scammers targeting accounting firm agent accounts to file bogus claims and reroute refunds into their own shady bank accounts.

That article turned on a lightbulb for her!

She went back through her records and found an email from a supposed new client, sent just before the breach happened. The client had attached a file - a zip folder, no less - claiming it contained her previous tax return. Inside was a sneaky little number pretending to be a PDF but in fact was an executable (.exe) file in disguise. She didn't run the file, but simply unzipping it had done enough damage. Talk about Trojan horse tactics.

Looking back, she describes feeling violated, confused, and - understandably - distrustful of every email attachment in her inbox. But with clarity came closure. She now knows what happened, and she shared her story with me so I could blog about it and reach others so they don't have to learn the hard way.

So what's the takeaway?

Be suspicious of files, especially zipped ones. Always double-check file extensions, too.  Something called 'pdf.exe' is not your friend. And remember, even the most cautious can get caught off guard.

Her final words? “I wish I hadn't had to learn this, but now that I have, I'll be soooo much more careful about what I open. I hope none of you have to go through this – stay safe out there!”

And that, dear readers, is a reminder that even with bookkeeping, spreadsheets and self-assessments, danger can come zipped and disguised. Be careful!

Until next time ...

ALISON MEAD
I'm your Bookkeeping Buddy: Discover more by clicking here!

Share the blog love ...

Buffer Facebook Twitter Linkedin Pinterest WhatsApp #cyberattack #cybersecurity #bookkeepers #dataprotection #scamawareness

About Alison Mead ...
Alison loves bookkeeping and supporting bookkeepers. She has been helping clients to be better bookkeepers in Sage 50 for over 24 years and has been Xero Accredited in accounts and payroll for a number of years too. She specialises in a very unique hand-holding method of training, helping bookkeepers and business owners to use their accounts software as and when they need support in setting up and producing their invoices, reports and financial information. Alison combines her role at Silicon Bullet with her Forever Living network marketing businesses and is often to be seen at business networking meetings as she likes to keep busy. You know what they say: if you want something done well ask a busy person!

More blog posts for you to enjoy ...
		Building Your Bookkeeping Business in 2026 The usual question I see asked in bookkeeping groups and forums is, where can I find customers, or how can I get experience now that I have passed my bookkeeping exams and started my bookkeeping business ......
		Why should you use a Bookkeeper? Keeping track of your accounts is a science as well as an art form. Yes, of course you can do it yourself, but wouldn't a bookkeeper make your life a whole lot easier? Having a clear picture of your finances at any given time...
		Making Tax Digital registration: Why you should act before HMRC does If you are required to use Making Tax Digital for Income Tax but haven't yet registered, my advice is simple: don't wait for HMRC to do it for you. Taking control of your Making Tax Digital registration now gives you the oppo...
		I've passed my Xero level 2 certification for another year While I'm certainly going to allow myself a little celebration, maintaining Xero certification for bookkeepers is about much more than having another certificate to display. For me, it's about demonstrating that the knowledge...
		Xero Classic Expenses is being retired in 2027 If your business still uses Xero Classic Expenses, there is an important change coming that is worth preparing for sooner rather than later. Xero has confirmed that its Classic Expenses feature will be retired in early 2027, ...
		MTD For Self Assessment: Don't panic if you missed the first deadline If you've recently discovered that the first Making Tax Digital (MTD) for Income Tax quarterly submission deadline has passed, don't panic. The first deadline, August 7, has passed, but there are currently no late-filing pena...
		Bookkeeping Buddy: Why DIY Bookkeeping Doesn't Mean Doing It Alone Many small business owners attempt DIY bookkeeping to save costs and maintain control. Yet, this path can be daunting. Learn how you can manage your finances more effectively with my Bookkeeping Buddy subscription, ensuring y...
		First MTD for Income Tax submissions: Early lessons from the front lines Making Tax Digital for Income Tax is now becoming a reality for many self-employed individuals and landlords. Bookkeepers across the country are beginning to complete their first quarterly submissions ......

Other bloggers you may like ...
		How to stay visible online without spending your time posting every day Posted by Steffi Lewis on https://www.sblogit.com For many small business owners, staying visible online feels like a full-time job. There's constant pressure to post on social media, keep websites up ...
		How multiple income streams helped me build a life I love Posted by Davina Farrer on https://blog.joindavina.co.uk I've always believed that multiple income streams can give you something incredibly valuable: choice. It isn't simply about earning more money. It's a ...
		What's Your Back Up Strategy? Posted by Pritesh Ganatra on https://blog.btsuk.net Here is the irony of the situation. It was inevitable that it would happen one day; that I would be caught out on the very thing I always preach to my ...
		Remote working gave people freedom, but less human contact Posted by Steffi Lewis on https://www.yourping.uk Remote work has transformed modern working life. For many, it has brought flexibility, reduced commuting costs and a better work-life balance. The fre ...