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!

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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!

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